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/__expo2.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) create mode 100644 src/math/__expo2.c (limited to 'src/math/__expo2.c') diff --git a/src/math/__expo2.c b/src/math/__expo2.c new file mode 100644 index 0000000..248f052 --- /dev/null +++ b/src/math/__expo2.c @@ -0,0 +1,17 @@ +#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) */ +double __expo2(double x, double sign) +{ + 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) */ + /* in directed rounding correct sign before rounding or overflow is important */ + return exp(x - kln2) * (sign * scale) * scale; +} -- cgit v1.2.3