first try at writing an efficient and "correct" exp10

[musl] / src / math / exp10l.c

diff --git a/src/math/exp10l.c b/src/math/exp10l.c
new file mode 100644 (file)
index 0000000..4d0c5a0
--- /dev/null
+++ b/src/math/exp10l.c
@@ -0,0 +1,19 @@
+#define _GNU_SOURCE
+#include <math.h>
+
+long double exp10l(long double x)
+{
+       static const long double p10[] = {
+               1e-15, 1e-14, 1e-13, 1e-12, 1e-11, 1e-10,
+               1e-9, 1e-8, 1e-7, 1e-6, 1e-5, 1e-4, 1e-3, 1e-2, 1e-1,
+               1, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9,
+               1e10, 1e11, 1e12, 1e13, 1e14, 1e15
+       };
+       long double n, y = modfl(x, &n);
+       if (fabsl(n) < 16) {
+               if (!y) return p10[(int)n+15];
+               y = exp2l(3.32192809488736234787031942948939L * y);
+               return y * p10[(int)n+15];
+       }
+       return powl(10.0, x);
+}