zig/lib/std/math/log.zig
Andrew Kelley ed36dbbd9c
mv std/ lib/
that's all this commit does. further commits will fix cli flags and
such.

see #2221
2019-09-25 23:35:41 -04:00

73 lines
2.5 KiB
Zig

// Ported from musl, which is licensed under the MIT license:
// https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
//
// https://git.musl-libc.org/cgit/musl/tree/src/math/logf.c
// https://git.musl-libc.org/cgit/musl/tree/src/math/log.c
const std = @import("../std.zig");
const math = std.math;
const builtin = @import("builtin");
const TypeId = builtin.TypeId;
const expect = std.testing.expect;
/// Returns the logarithm of x for the provided base.
pub fn log(comptime T: type, base: T, x: T) T {
if (base == 2) {
return math.log2(x);
} else if (base == 10) {
return math.log10(x);
} else if ((@typeId(T) == TypeId.Float or @typeId(T) == TypeId.ComptimeFloat) and base == math.e) {
return math.ln(x);
}
const float_base = math.lossyCast(f64, base);
switch (@typeId(T)) {
TypeId.ComptimeFloat => {
return @typeOf(1.0)(math.ln(f64(x)) / math.ln(float_base));
},
TypeId.ComptimeInt => {
return @typeOf(1)(math.floor(math.ln(f64(x)) / math.ln(float_base)));
},
builtin.TypeId.Int => {
// TODO implement integer log without using float math
return @floatToInt(T, math.floor(math.ln(@intToFloat(f64, x)) / math.ln(float_base)));
},
builtin.TypeId.Float => {
switch (T) {
f32 => return @floatCast(f32, math.ln(f64(x)) / math.ln(float_base)),
f64 => return math.ln(x) / math.ln(float_base),
else => @compileError("log not implemented for " ++ @typeName(T)),
}
},
else => {
@compileError("log expects integer or float, found '" ++ @typeName(T) ++ "'");
},
}
}
test "math.log integer" {
expect(log(u8, 2, 0x1) == 0);
expect(log(u8, 2, 0x2) == 1);
expect(log(i16, 2, 0x72) == 6);
expect(log(u32, 2, 0xFFFFFF) == 23);
expect(log(u64, 2, 0x7FF0123456789ABC) == 62);
}
test "math.log float" {
const epsilon = 0.000001;
expect(math.approxEq(f32, log(f32, 6, 0.23947), -0.797723, epsilon));
expect(math.approxEq(f32, log(f32, 89, 0.23947), -0.318432, epsilon));
expect(math.approxEq(f64, log(f64, 123897, 12389216414), 1.981724596, epsilon));
}
test "math.log float_special" {
expect(log(f32, 2, 0.2301974) == math.log2(f32(0.2301974)));
expect(log(f32, 10, 0.2301974) == math.log10(f32(0.2301974)));
expect(log(f64, 2, 213.23019799993) == math.log2(f64(213.23019799993)));
expect(log(f64, 10, 213.23019799993) == math.log10(f64(213.23019799993)));
}