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