Commit my changes to arith.c which fixed a couple of bugs and decreased
code size. Please read the TODO comments regarding accessing shell variables from the arith() funciton.
This commit is contained in:
Manuel Novoa III
parent
f6ecaccf92
commit
6a9d1f652b
398
libbb/arith.c
398
libbb/arith.c
@ -24,19 +24,88 @@
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* as a replacement for yacc-based parsers. However, it may well be faster
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* than a comparable parser writen in yacc. The supported operators are
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* listed in #defines below. Parens, order of operations, and error handling
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* are supported. This code is threadsafe. */
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* are supported. This code is threadsafe. The exact expression format should
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* be that which POSIX specifies for shells. */
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/* The code uses a simple two-stack algorithm. See
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* http://www.onthenet.com.au/~grahamis/int2008/week02/lect02.html
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* for a detailed explaination of the infix-to-postfix algorithm on which
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* this is based (this code differs in that it applies operators immediately
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* to the stack instead of adding them to a queue to end up with an
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* expression). */
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/* To use the routine, call it with an expression string and error return
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* pointer */
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/* To use the routine, call it with an expression string. It returns an
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* integer result. You will also need to define an "error" function
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* that takes printf arguments and _does not return_, or modify the code
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* to use another error mechanism. */
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/*
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* Aug 24, 2001 Manuel Novoa III
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*
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* Reduced the generated code size by about 30% (i386) and fixed several bugs.
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*
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* 1) In arith_apply():
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* a) Cached values of *numptr and &(numptr[-1]).
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* b) Removed redundant test for zero denominator.
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*
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* 2) In arith():
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* a) Eliminated redundant code for processing operator tokens by moving
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* to a table-based implementation. Also folded handling of parens
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* into the table.
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* b) Combined all 3 loops which called arith_apply to reduce generated
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* code size at the cost of speed.
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*
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* 3) The following expressions were treated as valid by the original code:
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* 1() , 0! , 1 ( *3 ) .
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* These bugs have been fixed by internally enclosing the expression in
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* parens and then checking that all binary ops and right parens are
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* preceded by a valid expression (NUM_TOKEN).
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*
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* Note: It may be desireable to replace Aaron's test for whitespace with
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* ctype's isspace() if it is used by another busybox applet or if additional
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* whitespace chars should be considered. Look below the "#include"s for a
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* precompiler test.
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*/
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/*
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* Aug 26, 2001 Manuel Novoa III
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*
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* Return 0 for null expressions. Pointed out by vodz.
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*
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* Merge in Aaron's comments previously posted to the busybox list,
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* modified slightly to take account of my changes to the code.
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*
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* TODO: May want to allow access to variables in the arith code.
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* This would:
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* 1) allow us to evaluate $A as 0 if A isn't set (although this
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* would require changes to ash.c too).
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* 2) allow us to write expressions as $(( A + 2 )).
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* This could be done using a callback function passed to the
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* arith() function of by requiring such a function with fixed
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* name as an extern.
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*/
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#include <stdlib.h>
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#include <string.h>
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#include <ctype.h>
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#include "libbb.h"
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/*
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* Use "#if 1" below for Aaron's original test for whitespace.
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* Use "#if 0" for ctype's isspace().
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* */
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#if 1
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#undef isspace
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#define isspace(arithval) \
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(arithval == ' ' || arithval == '\n' || arithval == '\t')
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#endif
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typedef char operator;
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/* An operator's token id is a bit of a bitfield. The lower 5 bits are the
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* precedence, and high 3 are an ID unique accross operators of that
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* precedence. The ID portion is so that multiple operators can have the
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* same precedence, ensuring that the leftmost one is evaluated first.
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* Consider * and /. */
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#define tok_decl(prec,id) (((id)<<5)|(prec))
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#define PREC(op) ((op)&0x1F)
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@ -70,194 +139,235 @@ typedef char operator;
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#define TOK_DIV tok_decl(10,1)
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#define TOK_REM tok_decl(10,2)
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/* For now all unary operators have the same precedence, and that's used to
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* identify them as unary operators */
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#define UNARYPREC 14
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#define TOK_BNOT tok_decl(UNARYPREC,0)
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#define TOK_NOT tok_decl(UNARYPREC,1)
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#define TOK_UMINUS tok_decl(UNARYPREC,2)
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#define TOK_UPLUS tok_decl(UNARYPREC,3)
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#define TOK_NUM tok_decl(15,0)
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#define TOK_RPAREN tok_decl(15,1)
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#define TOK_ERROR tok_decl(15,2) /* just a place-holder really */
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#define ARITH_APPLY(op) arith_apply(op, numstack, &numstackptr)
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#define NUMPTR (*numstackptr)
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/* "applying" a token means performing it on the top elements on the integer
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* stack. For a unary operator it will only change the top element, but a
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* binary operator will pop two arguments and push a result */
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static short arith_apply(operator op, long *numstack, long **numstackptr)
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{
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if (NUMPTR == numstack) goto err;
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if (op == TOK_UMINUS)
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NUMPTR[-1] *= -1;
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else if (op == TOK_NOT)
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NUMPTR[-1] = !(NUMPTR[-1]);
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else if (op == TOK_BNOT)
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NUMPTR[-1] = ~(NUMPTR[-1]);
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long numptr_val;
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long *NUMPTR_M1;
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if (NUMPTR == numstack) goto err; /* There is no operator that can work
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without arguments */
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NUMPTR_M1 = NUMPTR - 1;
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if (op == TOK_UMINUS)
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*NUMPTR_M1 *= -1;
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else if (op == TOK_NOT)
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*NUMPTR_M1 = !(*NUMPTR_M1);
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else if (op == TOK_BNOT)
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*NUMPTR_M1 = ~(*NUMPTR_M1);
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else if (op != TOK_UPLUS) {
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/* Binary operators */
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else {
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if (NUMPTR-1 == numstack) goto err;
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--NUMPTR;
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if (NUMPTR_M1 == numstack) goto err; /* ... and binary operators need two
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arguments */
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numptr_val = *--NUMPTR; /* ... and they pop one */
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NUMPTR_M1 = NUMPTR - 1;
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if (op == TOK_BOR)
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NUMPTR[-1] |= *NUMPTR;
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*NUMPTR_M1 |= numptr_val;
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else if (op == TOK_OR)
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NUMPTR[-1] = *NUMPTR || NUMPTR[-1];
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*NUMPTR_M1 = numptr_val || *NUMPTR_M1;
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else if (op == TOK_BAND)
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NUMPTR[-1] &= *NUMPTR;
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*NUMPTR_M1 &= numptr_val;
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else if (op == TOK_AND)
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NUMPTR[-1] = NUMPTR[-1] && *NUMPTR;
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*NUMPTR_M1 = *NUMPTR_M1 && numptr_val;
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else if (op == TOK_EQ)
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NUMPTR[-1] = (NUMPTR[-1] == *NUMPTR);
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*NUMPTR_M1 = (*NUMPTR_M1 == numptr_val);
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else if (op == TOK_NE)
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NUMPTR[-1] = (NUMPTR[-1] != *NUMPTR);
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*NUMPTR_M1 = (*NUMPTR_M1 != numptr_val);
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else if (op == TOK_GE)
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NUMPTR[-1] = (NUMPTR[-1] >= *NUMPTR);
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*NUMPTR_M1 = (*NUMPTR_M1 >= numptr_val);
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else if (op == TOK_RSHIFT)
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NUMPTR[-1] >>= *NUMPTR;
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*NUMPTR_M1 >>= numptr_val;
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else if (op == TOK_LSHIFT)
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NUMPTR[-1] <<= *NUMPTR;
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*NUMPTR_M1 <<= numptr_val;
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else if (op == TOK_GT)
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NUMPTR[-1] = (NUMPTR[-1] > *NUMPTR);
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*NUMPTR_M1 = (*NUMPTR_M1 > numptr_val);
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else if (op == TOK_LT)
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NUMPTR[-1] = (NUMPTR[-1] < *NUMPTR);
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*NUMPTR_M1 = (*NUMPTR_M1 < numptr_val);
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else if (op == TOK_LE)
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NUMPTR[-1] = (NUMPTR[-1] <= *NUMPTR);
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*NUMPTR_M1 = (*NUMPTR_M1 <= numptr_val);
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else if (op == TOK_MUL)
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NUMPTR[-1] *= *NUMPTR;
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else if (op == TOK_DIV) {
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if(*NUMPTR==0)
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return -2;
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NUMPTR[-1] /= *NUMPTR;
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}
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else if (op == TOK_REM) {
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if(*NUMPTR==0)
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return -2;
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NUMPTR[-1] %= *NUMPTR;
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}
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*NUMPTR_M1 *= numptr_val;
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else if (op == TOK_ADD)
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NUMPTR[-1] += *NUMPTR;
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*NUMPTR_M1 += numptr_val;
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else if (op == TOK_SUB)
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NUMPTR[-1] -= *NUMPTR;
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*NUMPTR_M1 -= numptr_val;
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else if(numptr_val==0) /* zero divisor check */
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return -2;
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else if (op == TOK_DIV)
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*NUMPTR_M1 /= numptr_val;
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else if (op == TOK_REM)
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*NUMPTR_M1 %= numptr_val;
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/* WARNING!!! WARNING!!! WARNING!!! */
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/* Any new operators should be added BEFORE the zero divisor check! */
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}
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return 0;
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err: return(-1);
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}
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extern long arith (const char *startbuf, int *errcode)
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{
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register char arithval;
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const char *expr = startbuf;
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static const char endexpression[] = ")";
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operator lasttok = TOK_MUL, op;
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size_t datasizes = strlen(startbuf);
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/* + and - (in that order) must be last */
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static const char op_char[] = "!<>=|&*/%~()+-";
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static const char op_token[] = {
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/* paired with equal */
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TOK_NE, TOK_LE, TOK_GE,
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/* paired with self -- note: ! is special-cased below*/
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TOK_ERROR, TOK_LSHIFT, TOK_RSHIFT, TOK_EQ, TOK_OR, TOK_AND,
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/* singles */
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TOK_NOT, TOK_LT, TOK_GT, TOK_ERROR, TOK_BOR, TOK_BAND,
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TOK_MUL, TOK_DIV, TOK_REM, TOK_BNOT, TOK_LPAREN, TOK_RPAREN,
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TOK_ADD, TOK_SUB, TOK_UPLUS, TOK_UMINUS
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};
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#define NUM_PAIR_EQUAL 3
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#define NUM_PAIR_SAME 6
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extern long arith (const char *expr, int *errcode)
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{
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register char arithval; /* Current character under analysis */
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operator lasttok, op;
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unsigned char prec;
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long *numstack, *numstackptr;
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operator *stack = alloca(datasizes * sizeof(operator)), *stackptr = stack;
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const char *p = endexpression;
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*errcode = 0;
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numstack = alloca((datasizes/2+1)*sizeof(long)), numstackptr = numstack;
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size_t datasizes = strlen(expr);
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while ((arithval = *expr)) {
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if (arithval == ' ' || arithval == '\n' || arithval == '\t')
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goto prologue;
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/* Stack of integers */
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/* The proof that there can be no more than strlen(startbuf)/2+1 integers
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* in any given correct or incorrect expression is left as an excersize to
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* the reader. */
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long *numstack = alloca((datasizes/2)*sizeof(long)),
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*numstackptr = numstack;
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/* Stack of operator tokens */
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operator *stack = alloca((datasizes+1) * sizeof(operator)),
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*stackptr = stack;
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*stackptr++ = lasttok = TOK_LPAREN; /* start off with a left paren */
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loop:
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if ((arithval = *expr) == 0) {
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if (p == endexpression) { /* Null expression. */
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return (*errcode = 0);
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}
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/* This is only reached after all tokens have been extracted from the
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* input stream. If there are still tokens on the operator stack, they
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* are to be applied in order. At the end, there should be a final
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* result on the integer stack */
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if (expr != endexpression + 1) { /* If we haven't done so already, */
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expr = endexpression; /* append a closing right paren */
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goto loop; /* and let the loop process it. */
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}
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/* At this point, we're done with the expression. */
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if (numstackptr != numstack+1) {/* ... but if there isn't, it's bad */
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err:
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return (*errcode = -1);
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/* NOTREACHED */
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}
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return *numstack;
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} else {
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/* Continue processing the expression. */
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if (isspace(arithval)) {
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goto prologue; /* Skip whitespace */
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}
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if ((unsigned)arithval-'0' <= 9) /* isdigit */ {
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*numstackptr++ = strtol(expr, (char **) &expr, 10);
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lasttok = TOK_NUM;
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continue;
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} if (arithval == '(') {
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*stackptr++ = TOK_LPAREN;
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lasttok = TOK_LPAREN;
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goto prologue;
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} if (arithval == ')') {
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lasttok = TOK_NUM;
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while (stackptr != stack) {
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op = *--stackptr;
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if (op == TOK_LPAREN)
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goto prologue;
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*errcode = ARITH_APPLY(op);
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if(*errcode) return *errcode;
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goto loop;
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}
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#if 1
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if ((p = strchr(op_char, arithval)) == NULL) {
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goto err;
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}
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#else
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for ( p=op_char ; *p != arithval ; p++ ) {
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if (!*p) {
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goto err;
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}
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goto err; /* Mismatched parens */
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} if (arithval == '|') {
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if (*++expr == '|')
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op = TOK_OR;
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else {
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}
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#endif
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p = op_token + (int)(p - op_char);
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++expr;
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if ((p >= op_token + NUM_PAIR_EQUAL) || (*expr != '=')) {
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p += NUM_PAIR_EQUAL;
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if ((p >= op_token + NUM_PAIR_SAME + NUM_PAIR_EQUAL)
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|| (*expr != arithval) || (arithval == '!')) {
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--expr;
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op = TOK_BOR;
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if (arithval == '=') { /* single = */
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goto err;
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}
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p += NUM_PAIR_SAME;
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/* Plus and minus are binary (not unary) _only_ if the last
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* token was as number, or a right paren (which pretends to be
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* a number, since it evaluates to one). Think about it.
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* It makes sense. */
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if ((lasttok != TOK_NUM)
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&& (p >= op_token + NUM_PAIR_SAME + NUM_PAIR_EQUAL
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+ sizeof(op_char) - 2)) {
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p += 2; /* Unary plus or minus */
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}
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}
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} else if (arithval == '&') {
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if (*++expr == '&')
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op = TOK_AND;
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else {
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--expr;
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op = TOK_BAND;
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}
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} else if (arithval == '=') {
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if (*++expr != '=') goto err; /* Unknown token */
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op = TOK_EQ;
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} else if (arithval == '!') {
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if (*++expr == '=')
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op = TOK_NE;
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else {
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--expr;
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op = TOK_NOT;
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}
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} else if (arithval == '>') {
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switch (*++expr) {
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case '=':
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op = TOK_GE;
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break;
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case '>':
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op = TOK_RSHIFT;
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break;
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default:
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--expr;
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op = TOK_GT;
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}
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} else if (arithval == '<') {
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switch (*++expr) {
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case '=':
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op = TOK_LE;
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break;
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case '<':
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op = TOK_LSHIFT;
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break;
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default:
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--expr;
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op = TOK_LT;
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}
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} else if (arithval == '*')
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op = TOK_MUL;
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else if (arithval == '/')
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op = TOK_DIV;
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else if (arithval == '%')
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op = TOK_REM;
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else if (arithval == '+') {
|
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if (lasttok != TOK_NUM) goto prologue; /* Unary plus */
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op = TOK_ADD;
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} else if (arithval == '-')
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op = (lasttok == TOK_NUM) ? TOK_SUB : TOK_UMINUS;
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else if (arithval == '~')
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op = TOK_BNOT;
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else goto err; /* Unknown token */
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}
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op = *p;
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||||
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/* We don't want a unary operator to cause recursive descent on the
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* stack, because there can be many in a row and it could cause an
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* operator to be evaluated before its argument is pushed onto the
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||||
* integer stack. */
|
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/* But for binary operators, "apply" everything on the operator
|
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* stack until we find an operator with a lesser priority than the
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* one we have just extracted. */
|
||||
/* Left paren is given the lowest priority so it will never be
|
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* "applied" in this way */
|
||||
prec = PREC(op);
|
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if (prec != UNARYPREC)
|
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while (stackptr != stack && PREC(stackptr[-1]) >= prec) {
|
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if ((prec > 0) && (prec != UNARYPREC)) { /* not left paren or unary */
|
||||
if (lasttok != TOK_NUM) { /* binary op must be preceded by a num */
|
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goto err;
|
||||
}
|
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while (stackptr != stack) {
|
||||
if (op == TOK_RPAREN) {
|
||||
/* The algorithm employed here is simple: while we don't
|
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* hit an open paren nor the bottom of the stack, pop
|
||||
* tokens and apply them */
|
||||
if (stackptr[-1] == TOK_LPAREN) {
|
||||
--stackptr;
|
||||
lasttok = TOK_NUM; /* Any operator directly after a */
|
||||
/* close paren should consider itself binary */
|
||||
goto prologue;
|
||||
}
|
||||
} else if (PREC(stackptr[-1]) < prec) {
|
||||
break;
|
||||
}
|
||||
*errcode = ARITH_APPLY(*--stackptr);
|
||||
if(*errcode) return *errcode;
|
||||
}
|
||||
*stackptr++ = op;
|
||||
lasttok = op;
|
||||
prologue: ++expr;
|
||||
} /* yay */
|
||||
if (op == TOK_RPAREN) {
|
||||
goto err;
|
||||
}
|
||||
}
|
||||
|
||||
while (stackptr != stack) {
|
||||
*errcode = ARITH_APPLY(*--stackptr);
|
||||
if(*errcode) return *errcode;
|
||||
}
|
||||
if (numstackptr != numstack+1) {
|
||||
err:
|
||||
*errcode = -1;
|
||||
return -1;
|
||||
/* NOTREACHED */
|
||||
}
|
||||
/* Push this operator to the stack and remember it. */
|
||||
*stackptr++ = lasttok = op;
|
||||
|
||||
return *numstack;
|
||||
prologue:
|
||||
++expr;
|
||||
goto loop;
|
||||
}
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue
Block a user