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std.math.sqrt_int: fixed odd size integers types

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Filippo Casarin 2021-03-24 20:59:15 +01:00 • committed by Veikka Tuominen
parent 13dc34f779
commit 8b0dbca32d
1 changed files with 27 additions and 32 deletions
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39
lib/std/math/sqrt.zig
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@ -39,15 +39,12 @@ pub fn sqrt(x: anytype) Sqrt(@TypeOf(x)) {
}
fn sqrt_int(comptime T: type, value: T) Sqrt(T) {
switch (T) {
u0 => return 0,
u1 => return value,
else => {},
}
if (@typeInfo(T).Int.bits <= 2) {
return if (value == 0) 0 else 1; // shortcut for small number of bits to simplify general case
} else {
var op = value;
var res: T = 0;
var one: T = 1 << (@typeInfo(T).Int.bits - 2);
var one: T = 1 << ((@typeInfo(T).Int.bits - 1) & -2); // highest power of four that fits into T
// "one" starts at the highest power of four <= than the argument.
while (one > op) {
@ -55,39 +52,37 @@ fn sqrt_int(comptime T: type, value: T) Sqrt(T) {
}
while (one != 0) {
if (op >= res + one) {
op -= res + one;
res += 2 * one;
}
var c = op >= res + one;
if (c) op -= res + one;
res >>= 1;
if (c) res += one;
one >>= 2;
}
const ResultType = Sqrt(T);
return @intCast(ResultType, res);
return @intCast(Sqrt(T), res);
}
}
test "math.sqrt_int" {
try expect(sqrt_int(u0, 0) == 0);
try expect(sqrt_int(u1, 1) == 1);
try expect(sqrt_int(u32, 3) == 1);
try expect(sqrt_int(u32, 4) == 2);
try expect(sqrt_int(u32, 5) == 2);
try expect(sqrt_int(u32, 8) == 2);
try expect(sqrt_int(u32, 9) == 3);
try expect(sqrt_int(u32, 10) == 3);
try expect(sqrt_int(u0, 0) == 0);
try expect(sqrt_int(u1, 1) == 1);
try expect(sqrt_int(u2, 3) == 1);
try expect(sqrt_int(u3, 4) == 2);
try expect(sqrt_int(u4, 8) == 2);
try expect(sqrt_int(u4, 9) == 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| {
return switch (int.bits) {
0 => u0,
1 => u1,
else => std.meta.Int(.unsigned, int.bits / 2),
};
},
.Int => |int| std.meta.Int(.unsigned, (int.bits + 1) / 2),
else => T,
};
}