From 4abab5ad6c8465a7528ccdd5f49367da05f78bbd Mon Sep 17 00:00:00 2001 From: Vladimir Azarov Date: Tue, 1 Oct 2024 15:47:05 +0200 Subject: Initial version --- src/math/__expo2f.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) create mode 100644 src/math/__expo2f.c (limited to 'src/math/__expo2f.c') diff --git a/src/math/__expo2f.c b/src/math/__expo2f.c new file mode 100644 index 0000000..538eb09 --- /dev/null +++ b/src/math/__expo2f.c @@ -0,0 +1,17 @@ +#include "libm.h" + +/* k is such that k*ln2 has minimal relative error and x - kln2 > log(FLT_MIN) */ +static const int k = 235; +static const float kln2 = 0x1.45c778p+7f; + +/* expf(x)/2 for x >= log(FLT_MAX), slightly better than 0.5f*expf(x/2)*expf(x/2) */ +float __expo2f(float x, float sign) +{ + float scale; + + /* note that k is odd and scale*scale overflows */ + SET_FLOAT_WORD(scale, (uint32_t)(0x7f + k/2) << 23); + /* exp(x - k ln2) * 2**(k-1) */ + /* in directed rounding correct sign before rounding or overflow is important */ + return expf(x - kln2) * (sign * scale) * scale; +} -- cgit v1.2.3