73 lines
2.0 KiB
Zig
73 lines
2.0 KiB
Zig
const std = @import("../std.zig");
|
|
const math = std.math;
|
|
const expect = std.testing.expect;
|
|
const builtin = @import("builtin");
|
|
const TypeId = builtin.TypeId;
|
|
const maxInt = std.math.maxInt;
|
|
|
|
/// Returns the square root of x.
|
|
///
|
|
/// Special Cases:
|
|
/// - sqrt(+inf) = +inf
|
|
/// - sqrt(+-0) = +-0
|
|
/// - sqrt(x) = nan if x < 0
|
|
/// - sqrt(nan) = nan
|
|
/// TODO Decide if all this logic should be implemented directly in the @sqrt bultin function.
|
|
pub fn sqrt(x: var) Sqrt(@TypeOf(x)) {
|
|
const T = @TypeOf(x);
|
|
switch (@typeInfo(T)) {
|
|
.Float, .ComptimeFloat => return @sqrt(x),
|
|
.ComptimeInt => comptime {
|
|
if (x > maxInt(u128)) {
|
|
@compileError("sqrt not implemented for comptime_int greater than 128 bits");
|
|
}
|
|
if (x < 0) {
|
|
@compileError("sqrt on negative number");
|
|
}
|
|
return @as(T, sqrt_int(u128, x));
|
|
},
|
|
.Int => return sqrt_int(T, x),
|
|
else => @compileError("sqrt not implemented for " ++ @typeName(T)),
|
|
}
|
|
}
|
|
|
|
fn sqrt_int(comptime T: type, value: T) std.meta.Int(false, T.bit_count / 2) {
|
|
var op = value;
|
|
var res: T = 0;
|
|
var one: T = 1 << (T.bit_count - 2);
|
|
|
|
// "one" starts at the highest power of four <= than the argument.
|
|
while (one > op) {
|
|
one >>= 2;
|
|
}
|
|
|
|
while (one != 0) {
|
|
if (op >= res + one) {
|
|
op -= res + one;
|
|
res += 2 * one;
|
|
}
|
|
res >>= 1;
|
|
one >>= 2;
|
|
}
|
|
|
|
const ResultType = std.meta.Int(false, T.bit_count / 2);
|
|
return @intCast(ResultType, res);
|
|
}
|
|
|
|
test "math.sqrt_int" {
|
|
expect(sqrt_int(u32, 3) == 1);
|
|
expect(sqrt_int(u32, 4) == 2);
|
|
expect(sqrt_int(u32, 5) == 2);
|
|
expect(sqrt_int(u32, 8) == 2);
|
|
expect(sqrt_int(u32, 9) == 3);
|
|
expect(sqrt_int(u32, 10) == 3);
|
|
}
|
|
|
|
/// Returns the return type `sqrt` will return given an operand of type `T`.
|
|
pub fn Sqrt(comptime T: type) type {
|
|
return switch (@typeInfo(T)) {
|
|
.Int => |int| std.meta.Int(false, int.bits / 2),
|
|
else => T,
|
|
};
|
|
}
|