65 lines
2.1 KiB
Zig
65 lines
2.1 KiB
Zig
const std = @import("../index.zig");
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const math = std.math;
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const builtin = @import("builtin");
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const TypeId = builtin.TypeId;
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const assert = std.debug.assert;
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pub fn log(comptime T: type, base: T, x: T) T {
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if (base == 2) {
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return math.log2(x);
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} else if (base == 10) {
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return math.log10(x);
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} else if ((@typeId(T) == TypeId.Float or @typeId(T) == TypeId.FloatLiteral) and base == math.e) {
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return math.ln(x);
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}
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switch (@typeId(T)) {
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TypeId.FloatLiteral => {
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return @typeOf(1.0)(math.ln(f64(x)) / math.ln(f64(base)));
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},
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TypeId.IntLiteral => {
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return @typeOf(1)(math.floor(math.ln(f64(x)) / math.ln(f64(base))));
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},
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builtin.TypeId.Int => {
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// TODO implement integer log without using float math
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return T(math.floor(math.ln(f64(x)) / math.ln(f64(base))));
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},
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builtin.TypeId.Float => {
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switch (T) {
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f32 => return f32(math.ln(f64(x)) / math.ln(f64(base))),
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f64 => return math.ln(x) / math.ln(f64(base)),
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else => @compileError("log not implemented for " ++ @typeName(T)),
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}
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},
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else => {
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@compileError("log expects integer or float, found '" ++ @typeName(T) ++ "'");
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},
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}
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}
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test "math.log integer" {
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assert(log(u8, 2, 0x1) == 0);
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assert(log(u8, 2, 0x2) == 1);
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assert(log(i16, 2, 0x72) == 6);
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assert(log(u32, 2, 0xFFFFFF) == 23);
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assert(log(u64, 2, 0x7FF0123456789ABC) == 62);
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}
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test "math.log float" {
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const epsilon = 0.000001;
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assert(math.approxEq(f32, log(f32, 6, 0.23947), -0.797723, epsilon));
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assert(math.approxEq(f32, log(f32, 89, 0.23947), -0.318432, epsilon));
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assert(math.approxEq(f64, log(f64, 123897, 12389216414), 1.981724596, epsilon));
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}
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test "math.log float_special" {
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assert(log(f32, 2, 0.2301974) == math.log2(f32(0.2301974)));
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assert(log(f32, 10, 0.2301974) == math.log10(f32(0.2301974)));
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assert(log(f64, 2, 213.23019799993) == math.log2(f64(213.23019799993)));
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assert(log(f64, 10, 213.23019799993) == math.log10(f64(213.23019799993)));
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}
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