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Faster writing of BCD representation

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This commit is contained in:
Niels Dossche 2024-05-20 14:44:37 +02:00
parent aef0eada16
commit 04a34c3433
1 changed files with 53 additions and 3 deletions
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56
ext/bcmath/libbcmath/src/recmul.c
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@ -112,6 +112,52 @@ static inline void bc_fast_mul(bc_num n1, size_t n1len, bc_num n2, size_t n2len,
}
}
#if BC_LITTLE_ENDIAN
# define BC_ENCODE_LUT(A, B) ((A) | (B) << 4)
#else
# define BC_ENCODE_LUT(A, B) ((B) | (A) << 4)
#endif
#define LUT_ITERATE(_, A) \
_(A, 0), _(A, 1), _(A, 2), _(A, 3), _(A, 4), _(A, 5), _(A, 6), _(A, 7), _(A, 8), _(A, 9)
/* This LUT encodes the decimal representation of numbers 0-100
* such that we can avoid taking modulos and divisions which would be slow. */
static const unsigned char LUT[100] = {
LUT_ITERATE(BC_ENCODE_LUT, 0),
LUT_ITERATE(BC_ENCODE_LUT, 1),
LUT_ITERATE(BC_ENCODE_LUT, 2),
LUT_ITERATE(BC_ENCODE_LUT, 3),
LUT_ITERATE(BC_ENCODE_LUT, 4),
LUT_ITERATE(BC_ENCODE_LUT, 5),
LUT_ITERATE(BC_ENCODE_LUT, 6),
LUT_ITERATE(BC_ENCODE_LUT, 7),
LUT_ITERATE(BC_ENCODE_LUT, 8),
LUT_ITERATE(BC_ENCODE_LUT, 9),
};
static inline unsigned short bc_expand_lut(unsigned char c)
{
return (c & 0x0f) | (c & 0xf0) << 4;
}
/* Writes the character representation of the number encoded in value.
* E.g. if value = 1234, then the string "1234" will be written to str. */
static void bc_write_bcd_representation(uint32_t value, char *str)
{
uint32_t upper = value / 100; /* e.g. 12 */
uint32_t lower = value % 100; /* e.g. 34 */
#if BC_LITTLE_ENDIAN
/* Note: little endian, so `lower` comes before `upper`! */
uint32_t digits = bc_expand_lut(LUT[lower]) << 16 | bc_expand_lut(LUT[upper]);
#else
/* Note: big endian, so `upper` comes before `lower`! */
uint32_t digits = bc_expand_lut(LUT[upper]) << 16 | bc_expand_lut(LUT[lower]);
#endif
memcpy(str, &digits, sizeof(digits));
}
/*
* Converts the BCD of bc_num by 4 (32 bits) or 8 (64 bits) digits to an array of BC_UINT_Ts.
* The array is generated starting with the smaller digits.
@ -180,9 +226,13 @@ static void bc_standard_mul(bc_num n1, size_t n1len, bc_num n2, size_t n2len, bc
char *pend = pptr + prodlen - 1;
i = 0;
while (i < prod_arr_size - 1) {
for (size_t j = 0; j < BC_MUL_UINT_DIGITS; j++) {
*pend-- = prod_uint[i] % BASE;
prod_uint[i] /= BASE;
if (BC_MUL_UINT_DIGITS == 4) {
bc_write_bcd_representation(prod_uint[i], pend - 3);
pend -= 4;
} else {
bc_write_bcd_representation(prod_uint[i] / 10000, pend - 7);
bc_write_bcd_representation(prod_uint[i] % 10000, pend - 3);
pend -= 8;
}
i++;
}