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1 #include "libm.h" | 1 #include "libm.h" |
2 | 2 |
3 /* k is such that k*ln2 has minimal relative error and x - kln2 > log(FLT_MIN) *
/ | 3 /* k is such that k*ln2 has minimal relative error and x - kln2 > log(FLT_MIN) |
| 4 */ |
4 static const int k = 235; | 5 static const int k = 235; |
5 static const float kln2 = 0x1.45c778p+7f; | 6 static const float kln2 = 0x1.45c778p+7f; |
6 | 7 |
7 /* expf(x)/2 for x >= log(FLT_MAX), slightly better than 0.5f*expf(x/2)*expf(x/2
) */ | 8 /* expf(x)/2 for x >= log(FLT_MAX), slightly better than |
8 float __expo2f(float x) | 9 * 0.5f*expf(x/2)*expf(x/2) */ |
9 { | 10 float __expo2f(float x) { |
10 » float scale; | 11 float scale; |
11 | 12 |
12 » /* note that k is odd and scale*scale overflows */ | 13 /* note that k is odd and scale*scale overflows */ |
13 » SET_FLOAT_WORD(scale, (uint32_t)(0x7f + k/2) << 23); | 14 SET_FLOAT_WORD(scale, (uint32_t)(0x7f + k / 2) << 23); |
14 » /* exp(x - k ln2) * 2**(k-1) */ | 15 /* exp(x - k ln2) * 2**(k-1) */ |
15 » return expf(x - kln2) * scale * scale; | 16 return expf(x - kln2) * scale * scale; |
16 } | 17 } |
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