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authorRich Felker <dalias@aerifal.cx>2012-04-30 03:26:53 -0400
committerRich Felker <dalias@aerifal.cx>2012-04-30 03:26:53 -0400
commitf6819755779a084bf2f82cb90175a4d9a018de73 (patch)
tree94048c26dd47a1f82507421df1d8815e14675197 /src/math
parent63374ee233c44891db80e6600d7a5a8c82e4ccca (diff)
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first try at writing an efficient and "correct" exp10
this is a nonstandard function so it's not clear what conditions it
should satisfy. my intent is that it be fast and exact for positive
integral exponents when the result fits in the destination type, and
fast and correctly rounded for small negative integral exponents.
otherwise we aim for at most 1ulp error; it seems to differ from pow
by at most 1ulp and it's often 2-5 times faster than pow.
Diffstat (limited to 'src/math')
-rw-r--r--src/math/exp10.c19
-rw-r--r--src/math/exp10f.c17
-rw-r--r--src/math/exp10l.c19
3 files changed, 55 insertions, 0 deletions
diff --git a/src/math/exp10.c b/src/math/exp10.c
new file mode 100644
index 00000000..7fd86fba
--- /dev/null
+++ b/src/math/exp10.c
@@ -0,0 +1,19 @@
+#define _GNU_SOURCE
+#include <math.h>
+
+double exp10(double x)
+{
+	static const 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
+	};
+	double n, y = modf(x, &n);
+	if (fabs(n) < 16) {
+		if (!y) return p10[(int)n+15];
+		y = exp2(3.32192809488736234787031942948939 * y);
+		return y * p10[(int)n+15];
+	}
+	return pow(10.0, x);
+}
diff --git a/src/math/exp10f.c b/src/math/exp10f.c
new file mode 100644
index 00000000..c9521411
--- /dev/null
+++ b/src/math/exp10f.c
@@ -0,0 +1,17 @@
+#define _GNU_SOURCE
+#include <math.h>
+
+float exp10f(float x)
+{
+	static const float p10[] = {
+		1e-7, 1e-6, 1e-5, 1e-4, 1e-3, 1e-2, 1e-1,
+		1, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7
+	};
+	float n, y = modff(x, &n);
+	if (fabsf(n) < 8) {
+		if (!y) return p10[(int)n+7];
+		y = exp2f(3.32192809488736234787031942948939f * y);
+		return y * p10[(int)n+7];
+	}
+	return exp2(3.32192809488736234787031942948939 * x);
+}
diff --git a/src/math/exp10l.c b/src/math/exp10l.c
new file mode 100644
index 00000000..4d0c5a01
--- /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);
+}