Skip to content

Add pow and powi support #23656

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 2 commits into
base: master
Choose a base branch
from
Open

Add pow and powi support #23656

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
82bd9c1
Added f16, f80, f128, comptime_float and comptime_int support to pow …
orejevich Apr 26, 2025
6b33a49
Added f16, f80, f128, comptime_float and comptime_int support to pow …
orejevich Apr 26, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
71 changes: 59 additions & 12 deletions lib/std/math/pow.zig
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -35,8 +35,12 @@ pub fn pow(comptime T: type, x: T, y: T) T {
return math.powi(T, x, y) catch unreachable;
}

if (T != f32 and T != f64) {
@compileError("pow not implemented for " ++ @typeName(T));
if (@typeInfo(T) == .comptime_float) {
return @as(comptime_float, pow(f128, @as(f128, x), @as(f128, y)));
}

if (@typeInfo(T) != .float) {
@compileError("pow only supports floating point types not " ++ @typeName(T));
}

// pow(x, +-0) = 1 for all x
Expand All @@ -60,15 +64,15 @@ pub fn pow(comptime T: type, x: T, y: T) T {
if (x == 0) {
if (y < 0) {
// pow(+-0, y) = +-inf for y an odd integer
if (isOddInteger(y)) {
if (isOddInteger(T, y)) {
return math.copysign(math.inf(T), x);
}
// pow(+-0, y) = +inf for y an even integer
else {
return math.inf(T);
}
} else {
if (isOddInteger(y)) {
if (isOddInteger(T, y)) {
return x;
} else {
return 0;
Expand Down Expand Up @@ -146,6 +150,7 @@ pub fn pow(comptime T: type, x: T, y: T) T {
var x1 = r2.significand;

var i = @as(std.meta.Int(.signed, @typeInfo(T).float.bits), @intFromFloat(yi));

while (i != 0) : (i >>= 1) {
const overflow_shift = math.floatExponentBits(T) + 1;
if (xe < -(1 << overflow_shift) or (1 << overflow_shift) < xe) {
Expand Down Expand Up @@ -178,8 +183,8 @@ pub fn pow(comptime T: type, x: T, y: T) T {
return math.scalbn(a1, ae);
}

fn isOddInteger(x: f64) bool {
if (@abs(x) >= 1 << 53) {
fn isOddInteger(comptime T: type, x: T) bool {
if (@abs(x) >= @as(T, @floatFromInt(1 << 53))) {
// From https://golang.org/src/math/pow.go
// 1 << 53 is the largest exact integer in the float64 format.
// Any number outside this range will be truncated before the decimal point and therefore will always be
Expand All @@ -188,15 +193,24 @@ fn isOddInteger(x: f64) bool {
return false;
}
const r = math.modf(x);
return r.fpart == 0.0 and @as(i64, @intFromFloat(r.ipart)) & 1 == 1;
return r.fpart == 0.0 and @as(i128, @intFromFloat(r.ipart)) & 1 == 1;
}

test isOddInteger {
try expect(isOddInteger(math.maxInt(i64) * 2) == false);
try expect(isOddInteger(math.maxInt(i64) * 2 + 1) == false);
try expect(isOddInteger(1 << 53) == false);
try expect(isOddInteger(12.0) == false);
try expect(isOddInteger(15.0) == true);
try expect(isOddInteger(f64, math.maxInt(i64) * 2) == false);
try expect(isOddInteger(f64, math.maxInt(i64) * 2 + 1) == false);
try expect(isOddInteger(f64, 1 << 53) == false);
try expect(isOddInteger(f64, 12.0) == false);
try expect(isOddInteger(f64, 15.0) == true);

try expect(isOddInteger(f16, @as(f16, 7.0)) == true);
try expect(isOddInteger(f16, @as(f16, 8.0)) == false);
try expect(isOddInteger(f80, @as(f80, 13.0)) == true);
try expect(isOddInteger(f80, @as(f80, 14.0)) == false);
try expect(isOddInteger(f128, @as(f128, 101.0)) == true);
try expect(isOddInteger(f128, @as(f128, 100.0)) == false);
try expect(isOddInteger(c_longdouble, @as(c_longdouble, 15.0)) == true);
try expect(isOddInteger(c_longdouble, @as(c_longdouble, 16.0)) == false);
}

test pow {
Expand All @@ -215,6 +229,25 @@ test pow {
try expect(math.approxEqAbs(f64, pow(f64, 1.5, 3.3), 3.811546, epsilon));
try expect(math.approxEqAbs(f64, pow(f64, 37.45, 3.3), 155736.7160616, epsilon));
try expect(math.approxEqAbs(f64, pow(f64, 89.123, 3.3), 2722490.231436, epsilon));
try expect(math.approxEqAbs(f16, pow(f16, 2, 4), 16.0, 0.1));
try expect(math.approxEqAbs(f80, pow(f80, 2, 4), 16.0, 0.00001));
try expect(math.approxEqAbs(f128, pow(f128, 2, 4), 16.0, 0.0000001));
try expect(math.approxEqAbs(c_longdouble, pow(c_longdouble, 2, 4), 16.0, 0.0000001));
}

test "pow with extended float types (f16, f80, f128, c_longdouble)" {
try expect(math.approxEqAbs(f16, pow(f16, 3.0, 3.0), 27.0, 0.5));
try expect(math.approxEqAbs(f16, pow(f16, 2.0, -1.0), 0.5, 0.01));
try expect(math.approxEqAbs(f80, pow(f80, 5.0, 0.5), @sqrt(@as(f80, 5.0)), 0.00001));
try expect(math.approxEqAbs(f128, pow(f128, 1.1, 2.2), 1.23328630055, 0.0000001));
try expect(math.approxEqAbs(c_longdouble, pow(c_longdouble, 9.0, 0.5), 3.0, 0.00001));

try expect(math.approxEqAbs(f16, pow(f16, 1.0, 0.0), 1.0, 0.01));
try expect(math.approxEqAbs(f16, pow(f16, 1.0, 1.0), 1.0, 0.01));
try expect(math.approxEqAbs(f80, pow(f80, 1.0, 0.0), 1.0, 0.00001));
try expect(math.approxEqAbs(f80, pow(f80, 1.0, 1.0), 1.0, 0.00001));
try expect(math.approxEqAbs(f128, pow(f128, 1.0, 0.0), 1.0, 0.0000001));
try expect(math.approxEqAbs(c_longdouble, pow(c_longdouble, 1.0, 0.0), 1.0, 0.0000001));
}

test "special" {
Expand Down Expand Up @@ -259,10 +292,24 @@ test "special" {
try expect(math.isNan(pow(f32, -12.4, 78.5)));
}

test "pow with extended float types: zero and negative base" {
try expect(math.isPositiveInf(pow(f80, 0.0, -3.0)));
try expect(pow(f80, 0.0, 3.0) == 0.0);
try expect(math.isNan(pow(f80, -2.0, 0.5)));
try expect(pow(f128, -2.0, 4.0) == 16.0);
}

test "overflow" {
try expect(math.isPositiveInf(pow(f64, 2, 1 << 32)));
try expect(pow(f64, 2, -(1 << 32)) == 0);
try expect(math.isNegativeInf(pow(f64, -2, (1 << 32) + 1)));
try expect(pow(f64, 0.5, 1 << 45) == 0);
try expect(math.isPositiveInf(pow(f64, 0.5, -(1 << 45))));

try expect(math.isPositiveInf(pow(f128, 10.0, 1 << 32)));
try expect(pow(f128, 10.0, -(1 << 32)) == 0.0);
try expect(math.isPositiveInf(pow(f80, 2.0, 1 << 32)));
try expect(pow(f80, 2.0, -(1 << 32)) == 0.0);
try expect(math.isPositiveInf(pow(f16, 2.0, 1 << 32)));
try expect(pow(f16, 2.0, -(1 << 32)) == 0.0);
}
58 changes: 58 additions & 0 deletions lib/std/math/powi.zig
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,41 @@ pub fn powi(comptime T: type, x: T, y: T) (error{
Overflow,
Underflow,
}!T) {
// Handle comptime_int separately
if (@typeInfo(T) == .comptime_int) {
if (y == 0) {
return 1;
}

if (x == 0) {
if (y > 0) {
return 0;
} else {
return error.Overflow;
}
}

if (y < 0) {
return error.Underflow;
}

var base = x;
var exp = y;
var acc: comptime_int = 1;

while (exp > 1) {
if (exp & 1 == 1) {
acc *= base;
}
exp >>= 1;
base *= base;
}
if (exp == 1) {
acc *= base;
}
return acc;
}

const bit_size = @typeInfo(T).int.bits;

// `y & 1 == 0` won't compile when `does_one_overflow`.
Expand Down Expand Up @@ -194,3 +229,26 @@ test "powi.narrow" {
try testing.expectError(error.Overflow, powi(i1, 0, -1));
try testing.expect((try powi(i1, -1, -1)) == -1);
}

test "powi.comptime" {
comptime {
try testing.expectEqual(1, try math.powi(comptime_int, 5, 0));
try testing.expectEqual(0, try math.powi(comptime_int, 0, 3));
try testing.expectError(error.Overflow, math.powi(comptime_int, 0, -2));

try testing.expectEqual(1, try math.powi(comptime_int, 1, 7));
try testing.expectEqual(-1, try math.powi(comptime_int, -1, 5));
try testing.expectEqual(1, try math.powi(comptime_int, -1, 4));

// Underflow check
try testing.expectError(error.Underflow, math.powi(comptime_int, 2, -1));

// Large value checks
const big_val = 12345678901234567890;
try testing.expectEqual(big_val, try math.powi(comptime_int, big_val, 1));

// Very large exponent (should succeed because comptime_int can grow)
const result = try math.powi(comptime_int, 2, 128);
try testing.expect(result > 0); // Just check it's positive
}
}
Loading