150 lines
4.5 KiB
Scheme
150 lines
4.5 KiB
Scheme
(library
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(regex)
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(export lit
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cat
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alt
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opt
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star
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plus
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compile-rx)
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(import (chezscheme)
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(loops)
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(matchable))
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;; Simple regex library, because it's friday and I'm bored.
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;; Playing with the ideas in: https://swtch.com/~rsc/regexp/regexp2.html
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;; which reminded me of reading through the source code to Sam in '93.
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;; Rather than parsing a string we'll use expressions.
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;; (lit <string>)
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;; (cat rx1 rx2)
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;; (alt rx1 rx2)
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;; (opt rx)
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;; (star rx)
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;; (plus rx)
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;;
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;; The expressions get compiled into a vector of vm instructions.
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;; (char c)
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;; (match)
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;; (jmp x)
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;; (split x y)
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;; instructions are closures that manipulate the thread
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;; FIXME: slow
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(define (append-instr code . i) (append code i))
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(define (label-instr l) `(label ,l))
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(define (jmp-instr l) `(jmp ,l))
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(define (char-instr c) `(char ,c))
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(define (split-instr l1 l2) `(split ,l1 ,l2))
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(define (match-instr) '(match))
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(define (match-instr? instr) (equal? '(match) instr))
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(define (label-code label code)
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(cons (label-instr label) code))
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;; Compiles to a list of labelled instructions that can later be flattened
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;; into a linear sequence.
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(define (lit str)
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(map char-instr (string->list str)))
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(define (cat rx1 rx2)
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(append rx1 rx2))
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(define (alt rx1 rx2)
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(let ((label1 (gensym))
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(label2 (gensym))
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(tail (gensym)))
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(let ((c1 (label-code label1
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(append-instr rx1 (jmp-instr tail))))
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(c2 (label-code label2 rx2)))
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(cons (split-instr label1 label2)
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(append-instr (append c1 c2) (label-instr tail))))))
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(define (opt rx)
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(let ((head (gensym))
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(tail (gensym)))
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(cons (split-instr head tail)
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(label-code head
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(append-instr rx (label-instr tail))))))
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(define (star rx)
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(let ((head (gensym))
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(tail (gensym)))
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(cons (split-instr head tail)
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(label-code head
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(append-instr rx
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(jmp-instr head)
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(label-instr tail))))))
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(define (plus rx)
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(let ((head (gensym))
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(tail (gensym)))
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(label-code head
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(append-instr rx
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(split-instr head tail)
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(label-instr tail)))))
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(define (label-locations code)
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(let ((locs (make-eq-hashtable)))
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(let loop ((pc 0)
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(code code))
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(if (null? code)
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locs
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(match (car code)
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(('label l)
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(begin
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(hashtable-set! locs l pc)
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(loop pc (cdr code))))
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(instr
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(loop (+ 1 pc) (cdr code))))))))
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(define (remove-labels code locs)
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(let loop ((pc 0)
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(code code)
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(acc '()))
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(if (null? code)
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(reverse acc)
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(match (car code)
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(('label l)
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(loop pc (cdr code) acc))
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(('jmp l)
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(loop (+ 1 pc) (cdr code)
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(cons `(jmp ,(hashtable-ref locs l #f)) acc)))
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(('split l1 l2)
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(loop (+ 1 pc) (cdr code)
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(cons `(split ,(hashtable-ref locs l1 #f)
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,(hashtable-ref locs l2 #f))
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acc)))
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(instr (loop (+ 1 pc) (cdr code) (cons instr acc)))))))
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(define (optimise-jumps! code)
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(upto (n (vector-length code))
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(match (vector-ref code n)
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(('jmp l)
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(when (match-instr? (vector-ref code l))
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(vector-set! code n (match-instr))))
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(('split l1 l2)
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(when (or (match-instr? (vector-ref code l1))
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(match-instr? (vector-ref code l2)))
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(vector-set! code n (match-instr))))
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(_ _)))
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code)
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(define (compile-rx rx)
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(let ((rx (append-instr rx (match-instr))))
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(optimise-jumps!
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(list->vector
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(remove-labels rx (label-locations rx))))))
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;; A 'thread' consists of an index into the instructions. A 'bundle' holds
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;; the current threads. Note there cannot be more threads than instructions,
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;; so a bundle is represented as a bitvector the same length as the
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;; instructions. Threads are run in lock step, all taking the same input.
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)
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