Index: fusl/src/math/__expo2f.c |
diff --git a/fusl/src/math/__expo2f.c b/fusl/src/math/__expo2f.c |
new file mode 100644 |
index 0000000000000000000000000000000000000000..5163e4180033b1ec45ac6cb5e159c4d607bb10dc |
--- /dev/null |
+++ b/fusl/src/math/__expo2f.c |
@@ -0,0 +1,16 @@ |
+#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 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) */ |
+ return expf(x - kln2) * scale * scale; |
+} |