Add math library

This covers the majority of the functions as covered by the C99
specification for a math library.

Code is adapted primarily from musl libc, with the pow and standard
trigonometric functions adapted from the Go stdlib.

Changes:

 - Remove assert expose in index and import as needed.
 - Add float log function and merge with existing base 2 integer
   implementation.

See https://github.com/tiehuis/zig-fmath.
See #374.

1 files changed, 70 insertions, 0 deletions

diff --git a/std/math/trunc.zig b/std/math/trunc.zig
new file mode 100644
index 0000000000..8c2c1b0496
--- /dev/null
+++ b/std/math/trunc.zig
@@ -0,0 +1,70 @@
+const math = @import("index.zig");
+const assert = @import("../debug.zig").assert;
+
+pub fn trunc(x: var) -> @typeOf(x) {
+    const T = @typeOf(x);
+    switch (T) {
+        f32 => @inlineCall(trunc32, x),
+        f64 => @inlineCall(trunc64, x),
+        else => @compileError("trunc not implemented for " ++ @typeName(T)),
+    }
+}
+
+fn trunc32(x: f32) -> f32 {
+    const u = @bitCast(u32, x);
+    var e = i32(((u >> 23) & 0xFF)) - 0x7F + 9;
+    var m: u32 = undefined;
+
+    if (e >= 23 + 9) {
+        return x;
+    }
+    if (e < 9) {
+        e = 1;
+    }
+
+    m = @maxValue(u32) >> u32(e);
+    if (u & m == 0) {
+        x
+    } else {
+        math.forceEval(x + 0x1p120);
+        @bitCast(f32, u & ~m)
+    }
+}
+
+fn trunc64(x: f64) -> f64 {
+    const u = @bitCast(u64, x);
+    var e = i32(((u >> 52) & 0x7FF)) - 0x3FF + 12;
+    var m: u64 = undefined;
+
+    if (e >= 52 + 12) {
+        return x;
+    }
+    if (e < 12) {
+        e = 1;
+    }
+
+    m = @maxValue(u64) >> u64(e);
+    if (u & m == 0) {
+        x
+    } else {
+        math.forceEval(x + 0x1p120);
+        @bitCast(f64, u & ~m)
+    }
+}
+
+test "trunc" {
+    assert(trunc(f32(1.3)) == trunc32(1.3));
+    assert(trunc(f64(1.3)) == trunc64(1.3));
+}
+
+test "trunc32" {
+    assert(trunc32(1.3) == 1.0);
+    assert(trunc32(-1.3) == -1.0);
+    assert(trunc32(0.2) == 0.0);
+}
+
+test "trunc64" {
+    assert(trunc64(1.3) == 1.0);
+    assert(trunc64(-1.3) == -1.0);
+    assert(trunc64(0.2) == 0.0);
+}