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https://gitlab.com/80486DX2-66/gists
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49 lines
2.3 KiB
C
49 lines
2.3 KiB
C
/*
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* opt_int_div.h
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*
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* "Optimized integer division"
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*
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* Author: Intel A80486DX2-66
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* License: Creative Commons Zero 1.0 Universal
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*/
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#include <math.h>
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#include <stdint.h>
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// parameters
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#define OPT_INT_DIV_TEST_PRECISION 8
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// constants
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#define OPT_INT_DIV_ROUNDING \
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/* 10^OPT_INT_DIV_TEST_PRECISION */ \
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powl(10.l, (long double) OPT_INT_DIV_TEST_PRECISION)
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// helper functions
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#define INT_BIN_DIV(a, b) ((a) >> (uintmax_t) log2l((b)))
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#define INT_DIV_NEG_RESULT_SIGN(a, b) (((a) < 0) ^ ((b) < 0))
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#define INT_ABS(x) ((x) < 0 ? -(x) : (x))
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// the main macro
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#define OPT_INT_DIV(a, b) \
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( /* beginning */ \
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/* check for equality of a and b */ \
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INT_ABS((a)) == INT_ABS((b)) ? \
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/* if only one of the numbers is negative, the result is -1, */ \
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/* otherwise it is 1. */ \
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(INT_DIV_NEG_RESULT_SIGN(a, b) ? -1 : 1) : ( \
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\
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/* check if b is a power of 2 */ \
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/* */ \
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/* formula: round(log_2(b) % 1, OPT_INT_DIV_TEST_PRECISION digits */ \
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/* after point) == 0 */ \
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(roundl(fmodl(log2l((b)), 1.l) * OPT_INT_DIV_ROUNDING) == 0.l) ? ( \
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/* if only one of the numbers is negative, the result is */ \
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/* negative */ \
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INT_DIV_NEG_RESULT_SIGN(a, b) ? \
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-INT_BIN_DIV(INT_ABS(a), INT_ABS(b)) \
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: \
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INT_BIN_DIV(INT_ABS(a), INT_ABS(b))) \
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: \
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((a) / (b)) ) \
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) /* end */
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