diff options
Diffstat (limited to 'libc-top-half/musl/src/math/__expo2.c')
| -rw-r--r-- | libc-top-half/musl/src/math/__expo2.c | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/libc-top-half/musl/src/math/__expo2.c b/libc-top-half/musl/src/math/__expo2.c new file mode 100644 index 0000000..4ff17df --- /dev/null +++ b/libc-top-half/musl/src/math/__expo2.c @@ -0,0 +1,25 @@ +#include "libm.h" + +/* k is such that k*ln2 has minimal relative error and x - kln2 > log(DBL_MIN) */ +static const int k = 2043; +static const double kln2 = 0x1.62066151add8bp+10; + +/* exp(x)/2 for x >= log(DBL_MAX), slightly better than 0.5*exp(x/2)*exp(x/2) */ +#ifdef __wasilibc_unmodified_upstream // Wasm doesn't have alternate rounding modes +double __expo2(double x, double sign) +#else +double __expo2(double x) +#endif +{ + double scale; + + /* note that k is odd and scale*scale overflows */ + INSERT_WORDS(scale, (uint32_t)(0x3ff + k/2) << 20, 0); + /* exp(x - k ln2) * 2**(k-1) */ +#ifdef __wasilibc_unmodified_upstream // Wasm doesn't have alternate rounding modes + /* in directed rounding correct sign before rounding or overflow is important */ + return exp(x - kln2) * (sign * scale) * scale; +#else + return exp(x - kln2) * scale * scale; +#endif +} |