Added logarithm functions for floats to std::math

Thanks to marijn for helping with #[link_name]

src/lib/math.rs

@@ -10,6 +10,11 @@ native mod libc {
     fn acos(n: float) -> float;
     fn tan(n: float) -> float;
     fn atan(n: float) -> float;
+    #[link_name="log"]
+    fn ln(n: float) -> float;
+    fn log2(n: float) -> float;
+    fn log10(n: float) -> float;
+    fn log1p(n: float) -> float;
 }
 
 /*
@@ -81,3 +86,40 @@ Function: max
 Returns the maximum of two values
 */
 fn max<copy T>(x: T, y: T) -> T { x < y ? y : x }
+
+/*
+Const: e
+
+Euler's number
+*/
+const e: float = 2.718281828459045235;
+
+/*
+Function: ln
+
+Returns the natural logaritm
+*/
+fn ln(n: float) -> float { libc::ln(n) }
+
+/*
+Function: log2
+
+Returns the logarithm to base 2
+*/
+fn log2(n: float) -> float { libc::log2(n) }
+
+/*
+Function: log2
+
+Returns the logarithm to base 10
+*/
+fn log10(n: float) -> float { libc::log10(n) }
+
+
+/*
+Function: log1p
+
+Returns the natural logarithm of `1+n` accurately, 
+even for very small values of `n`
+*/
+fn ln1p(n: float) -> float { libc::log1p(n) }

src/test/stdtest/math.rs

@@ -1,5 +1,6 @@
 use std;
 import std::math::*;
+import std::float;
 
 #[test]
 fn test_sqrt() {
@@ -32,3 +33,41 @@ fn test_angle() {
     assert angle((1f, 1f)) == 0.25 * pi;
     assert angle((0f, 1f)) == 0.5 * pi;
 }
+
+
+#[test]
+fn test_log_functions() {
+    assert ln(1.0) == 0.0;
+    assert log2(1.0) == 0.0;
+    assert log10(1.0) == 0.0;
+
+    assert ln(e) == 1.0;
+    assert log2(2.0) == 1.0;
+    assert log10(10.0) == 1.0;
+
+    assert ln(e*e*e*e) == 4.0;
+    assert log2(256.0) == 8.0;
+    assert log10(1000.0) == 3.0;
+
+    assert ln(0.0) == float::neg_infinity;
+    assert log2(0.0) == float::neg_infinity;
+    assert log10(0.0) == float::neg_infinity;
+
+    assert ln(-0.0) == float::neg_infinity;
+    assert log2(-0.0) == float::neg_infinity;
+    assert log10(-0.0) == float::neg_infinity;
+
+    assert float::isNaN(ln(-1.0));
+    assert float::isNaN(log2(-1.0));
+    assert float::isNaN(log10(-1.0));
+
+    assert ln(float::infinity) == float::infinity;
+    assert log2(float::infinity) == float::infinity;
+    assert log10(float::infinity) == float::infinity;
+
+    assert ln1p(0.0) == 0.0;
+    assert ln1p(-0.0) == 0.0;
+    assert ln1p(-1.0) == float::neg_infinity;
+    assert float::isNaN(ln1p(-2.0f));
+    assert ln1p(float::infinity) == float::infinity;
+}