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// Ported from musl, which is licensed under the MIT license:
// https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
//
// https://git.musl-libc.org/cgit/musl/tree/src/math/roundf.c
// https://git.musl-libc.org/cgit/musl/tree/src/math/round.c
const expect = std.testing.expect;
const std = @import("../std.zig");
const math = std.math;
/// Returns x rounded to the nearest integer, rounding half away from zero.
///
/// Special Cases:
/// - round(+-0) = +-0
/// - round(+-inf) = +-inf
/// - round(nan) = nan
pub fn round(x: anytype) @TypeOf(x) {
const T = @TypeOf(x);
return switch (T) {
f32 => round32(x),
f64 => round64(x),
f128 => round128(x),
// TODO this is not correct for some targets
c_longdouble => @floatCast(c_longdouble, round128(x)),
else => @compileError("round not implemented for " ++ @typeName(T)),
};
}
fn round32(x_: f32) f32 {
const f32_toint = 1.0 / math.floatEps(f32);
var x = x_;
const u = @bitCast(u32, x);
const e = (u >> 23) & 0xFF;
var y: f32 = undefined;
if (e >= 0x7F + 23) {
return x;
}
if (u >> 31 != 0) {
x = -x;
}
if (e < 0x7F - 1) {
math.doNotOptimizeAway(x + f32_toint);
return 0 * @bitCast(f32, u);
}
y = x + f32_toint - f32_toint - x;
if (y > 0.5) {
y = y + x - 1;
} else if (y <= -0.5) {
y = y + x + 1;
} else {
y = y + x;
}
if (u >> 31 != 0) {
return -y;
} else {
return y;
}
}
fn round64(x_: f64) f64 {
const f64_toint = 1.0 / math.floatEps(f64);
var x = x_;
const u = @bitCast(u64, x);
const e = (u >> 52) & 0x7FF;
var y: f64 = undefined;
if (e >= 0x3FF + 52) {
return x;
}
if (u >> 63 != 0) {
x = -x;
}
if (e < 0x3ff - 1) {
math.doNotOptimizeAway(x + f64_toint);
return 0 * @bitCast(f64, u);
}
y = x + f64_toint - f64_toint - x;
if (y > 0.5) {
y = y + x - 1;
} else if (y <= -0.5) {
y = y + x + 1;
} else {
y = y + x;
}
if (u >> 63 != 0) {
return -y;
} else {
return y;
}
}
fn round128(x_: f128) f128 {
const f128_toint = 1.0 / math.floatEps(f128);
var x = x_;
const u = @bitCast(u128, x);
const e = (u >> 112) & 0x7FFF;
var y: f128 = undefined;
if (e >= 0x3FFF + 112) {
return x;
}
if (u >> 127 != 0) {
x = -x;
}
if (e < 0x3FFF - 1) {
math.doNotOptimizeAway(x + f128_toint);
return 0 * @bitCast(f128, u);
}
y = x + f128_toint - f128_toint - x;
if (y > 0.5) {
y = y + x - 1;
} else if (y <= -0.5) {
y = y + x + 1;
} else {
y = y + x;
}
if (u >> 127 != 0) {
return -y;
} else {
return y;
}
}
test "math.round" {
try expect(round(@as(f32, 1.3)) == round32(1.3));
try expect(round(@as(f64, 1.3)) == round64(1.3));
try expect(round(@as(f128, 1.3)) == round128(1.3));
}
test "math.round32" {
try expect(round32(1.3) == 1.0);
try expect(round32(-1.3) == -1.0);
try expect(round32(0.2) == 0.0);
try expect(round32(1.8) == 2.0);
}
test "math.round64" {
try expect(round64(1.3) == 1.0);
try expect(round64(-1.3) == -1.0);
try expect(round64(0.2) == 0.0);
try expect(round64(1.8) == 2.0);
}
test "math.round128" {
try expect(round128(1.3) == 1.0);
try expect(round128(-1.3) == -1.0);
try expect(round128(0.2) == 0.0);
try expect(round128(1.8) == 2.0);
}
test "math.round32.special" {
try expect(round32(0.0) == 0.0);
try expect(round32(-0.0) == -0.0);
try expect(math.isPositiveInf(round32(math.inf(f32))));
try expect(math.isNegativeInf(round32(-math.inf(f32))));
try expect(math.isNan(round32(math.nan(f32))));
}
test "math.round64.special" {
try expect(round64(0.0) == 0.0);
try expect(round64(-0.0) == -0.0);
try expect(math.isPositiveInf(round64(math.inf(f64))));
try expect(math.isNegativeInf(round64(-math.inf(f64))));
try expect(math.isNan(round64(math.nan(f64))));
}
test "math.round128.special" {
try expect(round128(0.0) == 0.0);
try expect(round128(-0.0) == -0.0);
try expect(math.isPositiveInf(round128(math.inf(f128))));
try expect(math.isNegativeInf(round128(-math.inf(f128))));
try expect(math.isNan(round128(math.nan(f128))));
}
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