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// Ported from musl, which is MIT licensed.
// https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
//
// https://git.musl-libc.org/cgit/musl/tree/src/math/ilogbl.c
// https://git.musl-libc.org/cgit/musl/tree/src/math/ilogbf.c
// https://git.musl-libc.org/cgit/musl/tree/src/math/ilogb.c
const std = @import("../std.zig");
const math = std.math;
const expect = std.testing.expect;
const maxInt = std.math.maxInt;
const minInt = std.math.minInt;
/// Returns the binary exponent of x as an integer.
///
/// Special Cases:
/// - ilogb(+-inf) = maxInt(i32)
/// - ilogb(0) = maxInt(i32)
/// - ilogb(nan) = maxInt(i32)
pub fn ilogb(x: anytype) i32 {
const T = @TypeOf(x);
return switch (T) {
f32 => ilogb32(x),
f64 => ilogb64(x),
f128 => ilogb128(x),
else => @compileError("ilogb not implemented for " ++ @typeName(T)),
};
}
// TODO: unify these implementations with generics
// NOTE: Should these be exposed publicly?
const fp_ilogbnan = -1 - @as(i32, maxInt(u32) >> 1);
const fp_ilogb0 = fp_ilogbnan;
fn ilogb32(x: f32) i32 {
var u = @bitCast(u32, x);
var e = @intCast(i32, (u >> 23) & 0xFF);
// TODO: We should be able to merge this with the lower check.
if (math.isNan(x)) {
return maxInt(i32);
}
if (e == 0) {
u <<= 9;
if (u == 0) {
math.raiseInvalid();
return fp_ilogb0;
}
// subnormal
e = -0x7F;
while (u >> 31 == 0) : (u <<= 1) {
e -= 1;
}
return e;
}
if (e == 0xFF) {
math.raiseInvalid();
if (u << 9 != 0) {
return fp_ilogbnan;
} else {
return maxInt(i32);
}
}
return e - 0x7F;
}
fn ilogb64(x: f64) i32 {
var u = @bitCast(u64, x);
var e = @intCast(i32, (u >> 52) & 0x7FF);
if (math.isNan(x)) {
return maxInt(i32);
}
if (e == 0) {
u <<= 12;
if (u == 0) {
math.raiseInvalid();
return fp_ilogb0;
}
// subnormal
e = -0x3FF;
while (u >> 63 == 0) : (u <<= 1) {
e -= 1;
}
return e;
}
if (e == 0x7FF) {
math.raiseInvalid();
if (u << 12 != 0) {
return fp_ilogbnan;
} else {
return maxInt(i32);
}
}
return e - 0x3FF;
}
fn ilogb128(x: f128) i32 {
var u = @bitCast(u128, x);
var e = @intCast(i32, (u >> 112) & 0x7FFF);
if (math.isNan(x)) {
return maxInt(i32);
}
if (e == 0) {
u <<= 16;
if (u == 0) {
math.raiseInvalid();
return fp_ilogb0;
}
// subnormal x
return ilogb128(x * 0x1p120) - 120;
}
if (e == 0x7FFF) {
math.raiseInvalid();
if (u << 16 != 0) {
return fp_ilogbnan;
} else {
return maxInt(i32);
}
}
return e - 0x3FFF;
}
test "type dispatch" {
try expect(ilogb(@as(f32, 0.2)) == ilogb32(0.2));
try expect(ilogb(@as(f64, 0.2)) == ilogb64(0.2));
}
test "32" {
try expect(ilogb32(0.0) == fp_ilogb0);
try expect(ilogb32(0.5) == -1);
try expect(ilogb32(0.8923) == -1);
try expect(ilogb32(10.0) == 3);
try expect(ilogb32(-123984) == 16);
try expect(ilogb32(2398.23) == 11);
}
test "64" {
try expect(ilogb64(0.0) == fp_ilogb0);
try expect(ilogb64(0.5) == -1);
try expect(ilogb64(0.8923) == -1);
try expect(ilogb64(10.0) == 3);
try expect(ilogb64(-123984) == 16);
try expect(ilogb64(2398.23) == 11);
}
test "128" {
try expect(ilogb128(0.0) == fp_ilogb0);
try expect(ilogb128(0.5) == -1);
try expect(ilogb128(0.8923) == -1);
try expect(ilogb128(10.0) == 3);
try expect(ilogb128(-123984) == 16);
try expect(ilogb128(2398.23) == 11);
}
test "32 special" {
try expect(ilogb32(math.inf(f32)) == maxInt(i32));
try expect(ilogb32(-math.inf(f32)) == maxInt(i32));
try expect(ilogb32(0.0) == minInt(i32));
try expect(ilogb32(math.nan(f32)) == maxInt(i32));
}
test "64 special" {
try expect(ilogb64(math.inf(f64)) == maxInt(i32));
try expect(ilogb64(-math.inf(f64)) == maxInt(i32));
try expect(ilogb64(0.0) == minInt(i32));
try expect(ilogb64(math.nan(f64)) == maxInt(i32));
}
test "128 special" {
try expect(ilogb128(math.inf(f128)) == maxInt(i32));
try expect(ilogb128(-math.inf(f128)) == maxInt(i32));
try expect(ilogb128(0.0) == minInt(i32));
try expect(ilogb128(math.nan(f128)) == maxInt(i32));
}
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