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Add integer rotation functions

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This commit is contained in:
Marc Tiehuis 2018-01-13 13:23:12 +13:00
parent 3268276b58
commit 304f6f1d01
1 changed files with 39 additions and 0 deletions
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39
std/math/index.zig
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@ -267,6 +267,45 @@ test "math.shr" {
assert(shr(u8, 0b11111111, isize(-2)) == 0b11111100);
}
/// Rotates right. Only unsigned values can be rotated.
/// Negative shift values results in shift modulo the bit count.
pub fn rotr(comptime T: type, x: T, r: var) -> T {
if (T.is_signed) {
@compileError("cannot rotate signed integer");
} else {
const ar = @mod(r, T.bit_count);
return shr(T, x, ar) | shl(T, x, T.bit_count - ar);
}
}
test "math.rotr" {
assert(rotr(u8, 0b00000001, usize(0)) == 0b00000001);
assert(rotr(u8, 0b00000001, usize(9)) == 0b10000000);
assert(rotr(u8, 0b00000001, usize(8)) == 0b00000001);
assert(rotr(u8, 0b00000001, usize(4)) == 0b00010000);
assert(rotr(u8, 0b00000001, isize(-1)) == 0b00000010);
}
/// Rotates left. Only unsigned values can be rotated.
/// Negative shift values results in shift modulo the bit count.
pub fn rotl(comptime T: type, x: T, r: var) -> T {
if (T.is_signed) {
@compileError("cannot rotate signed integer");
} else {
const ar = @mod(r, T.bit_count);
return shl(T, x, ar) | shr(T, x, T.bit_count - ar);
}
}
test "math.rotl" {
assert(rotl(u8, 0b00000001, usize(0)) == 0b00000001);
assert(rotl(u8, 0b00000001, usize(9)) == 0b00000010);
assert(rotl(u8, 0b00000001, usize(8)) == 0b00000001);
assert(rotl(u8, 0b00000001, usize(4)) == 0b00010000);
assert(rotl(u8, 0b00000001, isize(-1)) == 0b10000000);
}
pub fn Log2Int(comptime T: type) -> type {
return @IntType(false, log2(T.bit_count));
}