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std.math: Clarify ceilPowerOfTwo inputs and disallow zero as an input

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This commit is contained in:
Ryan Liptak 2019-06-04 15:49:27 -07:00
parent 9bed6e1bf9
commit a0d66fa1e6
1 changed files with 7 additions and 9 deletions
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16
std/math.zig
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@ -706,23 +706,23 @@ fn testFloorPowerOfTwo() void {
}
/// Returns the next power of two (if the value is not already a power of two).
/// Only unsigned integers can be used. Zero is not an allowed input.
/// Result is a type with 1 more bit than the input type.
pub fn ceilPowerOfTwoPromote(comptime T: type, value: T) @IntType(T.is_signed, T.bit_count + 1) {
if (T.is_signed) {
@compileError("signed integers not supported");
}
comptime assert(@typeId(T) == builtin.TypeId.Int);
comptime assert(!T.is_signed);
assert(value != 0);
comptime const promotedType = @IntType(T.is_signed, T.bit_count + 1);
comptime const shiftType = std.math.Log2Int(promotedType);
if (value == 0) return promotedType(0);
return promotedType(1) << @intCast(shiftType, T.bit_count - @clz(T, value - 1));
}
/// Returns the next power of two (if the value is not already a power of two).
/// Only unsigned integers can be used. Zero is not an allowed input.
/// If the value doesn't fit, returns an error.
pub fn ceilPowerOfTwo(comptime T: type, value: T) (error{Overflow}!T) {
if (T.is_signed) {
@compileError("signed integers not supported");
}
comptime assert(@typeId(T) == builtin.TypeId.Int);
comptime assert(!T.is_signed);
comptime const promotedType = @IntType(T.is_signed, T.bit_count + 1);
comptime const overflowBit = promotedType(1) << T.bit_count;
var x = ceilPowerOfTwoPromote(T, value);
@ -738,7 +738,6 @@ test "math.ceilPowerOfTwoPromote" {
}
fn testCeilPowerOfTwoPromote() void {
testing.expectEqual(u33(0), ceilPowerOfTwoPromote(u32, 0));
testing.expectEqual(u33(1), ceilPowerOfTwoPromote(u32, 1));
testing.expectEqual(u33(2), ceilPowerOfTwoPromote(u32, 2));
testing.expectEqual(u33(64), ceilPowerOfTwoPromote(u32, 63));
@ -756,7 +755,6 @@ test "math.ceilPowerOfTwo" {
}
fn testCeilPowerOfTwo() !void {
testing.expectEqual(u32(0), try ceilPowerOfTwo(u32, 0));
testing.expectEqual(u32(1), try ceilPowerOfTwo(u32, 1));
testing.expectEqual(u32(2), try ceilPowerOfTwo(u32, 2));
testing.expectEqual(u32(64), try ceilPowerOfTwo(u32, 63));