Index: fusl/src/math/__expo2.c |
diff --git a/fusl/src/math/__expo2.c b/fusl/src/math/__expo2.c |
new file mode 100644 |
index 0000000000000000000000000000000000000000..740ac680e857070c950d4e0d52d019ad4c225ab6 |
--- /dev/null |
+++ b/fusl/src/math/__expo2.c |
@@ -0,0 +1,16 @@ |
+#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 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) */ |
+ return exp(x - kln2) * scale * scale; |
+} |