mirror of
https://gitlab.com/80486DX2-66/gists
synced 2024-11-08 18:02:23 +05:30
59 lines
3.1 KiB
C
59 lines
3.1 KiB
C
/*
|
|
* opt_int_div.h
|
|
*
|
|
* "Optimized integer division"
|
|
*
|
|
* Author: Intel A80486DX2-66
|
|
* License: Creative Commons Zero 1.0 Universal
|
|
*/
|
|
|
|
#include <math.h>
|
|
#include <stdint.h>
|
|
|
|
// parameters
|
|
#define OPT_INT_DIV_IS_TEST_PRECISION_LIMITED 0 /* true (1) or false (0) */
|
|
#define OPT_INT_DIV_TEST_PRECISION 8 /* only if the above parameter is 1 */
|
|
|
|
// constants
|
|
#define OPT_INT_DIV_ROUNDING \
|
|
/* formula: 10^OPT_INT_DIV_TEST_PRECISION */ \
|
|
powl(10.l, (long double) OPT_INT_DIV_TEST_PRECISION)
|
|
|
|
// helper functions
|
|
#define INT_BIN_DIV(a, b) ((a) >> (uintmax_t) log2l((b)))
|
|
#define INT_DIV_NEG_RESULT_SIGN(a, b) \
|
|
/* the sign is negative only if one of the numbers is negative */ \
|
|
(((a) < 0) ^ ((b) < 0)) /* 1 if sign is negative else 0 */
|
|
#define INT_ABS(x) ((x) < 0 ? -(x) : (x))
|
|
#define LOG2_DEC_PORTION(b) fmodl(log2l(INT_ABS((b))), 1.l)
|
|
#define OPT_INT_DIV_TEST(b) \
|
|
/* check if b is a power of 2 */ \
|
|
/* */ \
|
|
/* formula: round(log_2(b) % 1, OPT_INT_DIV_TEST_PRECISION digits */ \
|
|
/* after point) == 0 */ \
|
|
OPT_INT_DIV_IS_TEST_PRECISION_LIMITED ? \
|
|
roundl(LOG2_DEC_PORTION((b)) * OPT_INT_DIV_ROUNDING) == 0.l \
|
|
: \
|
|
LOG2_DEC_PORTION((b)) == 0.l
|
|
|
|
// the main macro
|
|
#define OPT_INT_DIV(a, b) \
|
|
( /* beginning */ \
|
|
/* check for equality of a and b */ \
|
|
INT_ABS((a)) == INT_ABS((b)) ? \
|
|
/* the result is +/-1 */ \
|
|
(INT_DIV_NEG_RESULT_SIGN(a, b) ? -1 : 1) : ( \
|
|
\
|
|
/* check if abs(a) < abs(b) */ \
|
|
INT_ABS((a)) < INT_ABS((b)) ? \
|
|
0 : ( \
|
|
\
|
|
OPT_INT_DIV_TEST((b)) ? \
|
|
(INT_DIV_NEG_RESULT_SIGN(a, b) ? \
|
|
-INT_BIN_DIV(INT_ABS((a)), INT_ABS((b))) \
|
|
: \
|
|
INT_BIN_DIV(INT_ABS((a)), INT_ABS((b)))) \
|
|
: \
|
|
((a) / (b)) )) \
|
|
) /* end */
|