source:
asp3_tinet_ecnl_arm/trunk/musl-1.1.18/src/math/__expo2.c
Last change on this file was 352, checked in by , 6 years ago | |
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File size: 485 bytes |
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1 | #include "libm.h" |
2 | |
3 | /* k is such that k*ln2 has minimal relative error and x - kln2 > log(DBL_MIN) */ |
4 | static const int k = 2043; |
5 | static const double kln2 = 0x1.62066151add8bp+10; |
6 | |
7 | /* exp(x)/2 for x >= log(DBL_MAX), slightly better than 0.5*exp(x/2)*exp(x/2) */ |
8 | double __expo2(double x) |
9 | { |
10 | double scale; |
11 | |
12 | /* note that k is odd and scale*scale overflows */ |
13 | INSERT_WORDS(scale, (uint32_t)(0x3ff + k/2) << 20, 0); |
14 | /* exp(x - k ln2) * 2**(k-1) */ |
15 | return exp(x - kln2) * scale * scale; |
16 | } |
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