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[number] Optimize _pow10 constants (#1963)

This commit is contained in:
Ebrahim Byagowi 2019-09-09 00:28:16 +04:30 committed by GitHub
parent 3f2cdf07a4
commit 30e5cdfbf1
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 32 additions and 42 deletions
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43
src/hb-number-parser.hh
View File

@ -96,28 +96,23 @@ static const int double_parser_en_main = 1;
#line 70 "hb-number-parser.rl" #line 70 "hb-number-parser.rl"
constexpr double _pow2 (double x) { return x * x; }
constexpr double _pow10_of_2i (unsigned int n)
{ return n == 1 ? 10. : _pow2 (_pow10_of_2i (n >> 1)); }
static const double _powers_of_10[] =
{
_pow10_of_2i (0x100),
_pow10_of_2i (0x80),
_pow10_of_2i (0x40),
_pow10_of_2i (0x20),
_pow10_of_2i (0x10),
_pow10_of_2i (0x8),
_pow10_of_2i (0x4),
_pow10_of_2i (0x2),
_pow10_of_2i (0x1),
};
/* Works only for n < 512 */ /* Works only for n < 512 */
inline double inline double
_pow10 (unsigned int exponent) _pow10 (unsigned int exponent)
{ {
unsigned int mask = 0x100; /* Should be same with the first element */ static const double _powers_of_10[] =
{
1.0e+256,
1.0e+128,
1.0e+64,
1.0e+32,
1.0e+16,
1.0e+8,
10000.,
100.,
10.
};
unsigned int mask = 1 << (ARRAY_LENGTH (_powers_of_10) - 1);
double result = 1; double result = 1;
for (const double *power = _powers_of_10; mask; ++power, mask >>= 1) for (const double *power = _powers_of_10; mask; ++power, mask >>= 1)
if (exponent & mask) result *= *power; if (exponent & mask) result *= *power;
@ -143,12 +138,12 @@ strtod_rl (const char *buf, char **end_ptr)
int cs; int cs;
#line 147 "hb-number-parser.hh" #line 142 "hb-number-parser.hh"
{ {
cs = double_parser_start; cs = double_parser_start;
} }
#line 152 "hb-number-parser.hh" #line 147 "hb-number-parser.hh"
{ {
int _slen; int _slen;
int _trans; int _trans;
@ -206,7 +201,7 @@ _resume:
exp_overflow = true; exp_overflow = true;
} }
break; break;
#line 210 "hb-number-parser.hh" #line 205 "hb-number-parser.hh"
} }
_again: _again:
@ -218,7 +213,7 @@ _again:
_out: {} _out: {}
} }
#line 121 "hb-number-parser.rl" #line 116 "hb-number-parser.rl"
*end_ptr = (char *) p; *end_ptr = (char *) p;
@ -229,8 +224,8 @@ _again:
if (unlikely (exp_overflow)) if (unlikely (exp_overflow))
{ {
if (value == 0) return value; if (value == 0) return value;
if (exp_neg) return neg ? -DBL_MIN : DBL_MIN; if (exp_neg) return neg ? -DBL_MIN : DBL_MIN;
else return neg ? -DBL_MAX : DBL_MAX; else return neg ? -DBL_MAX : DBL_MAX;
} }
if (exp) if (exp)

31
src/hb-number-parser.rl
View File

@ -69,28 +69,23 @@ main := (
}%% }%%
constexpr double _pow2 (double x) { return x * x; }
constexpr double _pow10_of_2i (unsigned int n)
{ return n == 1 ? 10. : _pow2 (_pow10_of_2i (n >> 1)); }
static const double _powers_of_10[] =
{
_pow10_of_2i (0x100),
_pow10_of_2i (0x80),
_pow10_of_2i (0x40),
_pow10_of_2i (0x20),
_pow10_of_2i (0x10),
_pow10_of_2i (0x8),
_pow10_of_2i (0x4),
_pow10_of_2i (0x2),
_pow10_of_2i (0x1),
};
/* Works only for n < 512 */ /* Works only for n < 512 */
inline double inline double
_pow10 (unsigned int exponent) _pow10 (unsigned int exponent)
{ {
unsigned int mask = 0x100; /* Should be same with the first element */ static const double _powers_of_10[] =
{
1.0e+256,
1.0e+128,
1.0e+64,
1.0e+32,
1.0e+16,
1.0e+8,
10000.,
100.,
10.
};
unsigned int mask = 1 << (ARRAY_LENGTH (_powers_of_10) - 1);
double result = 1; double result = 1;
for (const double *power = _powers_of_10; mask; ++power, mask >>= 1) for (const double *power = _powers_of_10; mask; ++power, mask >>= 1)
if (exponent & mask) result *= *power; if (exponent & mask) result *= *power;