const std = @import("../std.zig");
const math = std.math;
const expect = std.testing.expect;
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 ((@typeInfo(T) == .Float or @typeInfo(T) == .ComptimeFloat) and base == math.e) {
return @log(x);
}
const float_base = math.lossyCast(f64, base);
switch (@typeInfo(T)) {
.ComptimeFloat => {
return @as(comptime_float, @log(@as(f64, x)) / @log(float_base));
},
.ComptimeInt => {
return @as(comptime_int, @floor(@log(@as(f64, x)) / @log(float_base)));
},
.Int => |IntType| switch (IntType.signedness) {
.signed => @compileError("log not implemented for signed integers"),
.unsigned => return @floatToInt(T, @floor(@log(@intToFloat(f64, x)) / @log(float_base))),
},
.Float => {
switch (T) {
f32 => return @floatCast(f32, @log(@as(f64, x)) / @log(float_base)),
f64 => return @log(x) / @log(float_base),
else => @compileError("log not implemented for " ++ @typeName(T)),
}
},
else => {
@compileError("log expects integer or float, found '" ++ @typeName(T) ++ "'");
},
}
}
test "math.log integer" {
try expect(log(u8, 2, 0x1) == 0);
try expect(log(u8, 2, 0x2) == 1);
try expect(log(u16, 2, 0x72) == 6);
try expect(log(u32, 2, 0xFFFFFF) == 23);
try expect(log(u64, 2, 0x7FF0123456789ABC) == 62);
}
test "math.log float" {
const epsilon = 0.000001;
try expect(math.approxEqAbs(f32, log(f32, 6, 0.23947), -0.797723, epsilon));
try expect(math.approxEqAbs(f32, log(f32, 89, 0.23947), -0.318432, epsilon));
try expect(math.approxEqAbs(f64, log(f64, 123897, 12389216414), 1.981724596, epsilon));
}
test "math.log float_special" {
try expect(log(f32, 2, 0.2301974) == math.log2(@as(f32, 0.2301974)));
try expect(log(f32, 10, 0.2301974) == math.log10(@as(f32, 0.2301974)));
try expect(log(f64, 2, 213.23019799993) == math.log2(@as(f64, 213.23019799993)));
try expect(log(f64, 10, 213.23019799993) == math.log10(@as(f64, 213.23019799993)));
}