1 files changed, 25 insertions, 0 deletions
diff --git a/libc-top-half/musl/src/math/__expo2f.c b/libc-top-half/musl/src/math/__expo2f.c
new file mode 100644
index 0000000..acbaeb4
--- /dev/null
+++ b/libc-top-half/musl/src/math/__expo2f.c
@@ -0,0 +1,25 @@
+#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) */
+#ifdef __wasilibc_unmodified_upstream // Wasm doesn't have alternate rounding modes
+float __expo2f(float x, float sign)
+#else
+float __expo2f(float x)
+#endif
+{
+	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) */
+#ifdef __wasilibc_unmodified_upstream // Wasm doesn't have alternate rounding modes
+	/* in directed rounding correct sign before rounding or overflow is important */
+	return expf(x - kln2) * (sign * scale) * scale;
+#else
+	return expf(x - kln2) * scale * scale;
+#endif
+}