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https://gitlab.com/80486DX2-66/gists
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61 lines
3.1 KiB
C
61 lines
3.1 KiB
C
/*
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* opt_int_div.h
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*
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* "Optimized integer division": A header-only library
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*
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* NOTE: This code will work only on a computer that uses bits.
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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_IS_TEST_PRECISION_LIMITED 0 /* true (1) or false (0) */
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#define OPT_INT_DIV_TEST_PRECISION 8 /* only if the above parameter is 1 */
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// constants
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#define OPT_INT_DIV_ROUNDING \
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/* formula: 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) \
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/* the sign is negative only if one of the numbers is negative */ \
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(((a) < 0) != ((b) < 0)) /* 1 if sign is negative else 0 */
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#define INT_ABS(x) ((x) < 0 ? -(x) : (x))
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#define LOG2_DEC_PORTION(b) fmodl(log2l(INT_ABS((b))), 1.l)
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#define OPT_INT_DIV_TEST(b) \
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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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OPT_INT_DIV_IS_TEST_PRECISION_LIMITED ? \
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roundl(LOG2_DEC_PORTION((b)) * OPT_INT_DIV_ROUNDING) == 0.l \
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: \
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LOG2_DEC_PORTION((b)) == 0.l
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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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/* the result 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 abs(a) < abs(b) */ \
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INT_ABS((a)) < INT_ABS((b)) ? \
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0 : ( \
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\
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OPT_INT_DIV_TEST((b)) ? \
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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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