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// Special Cases:
//
// - ilogb(+-inf) = maxInt(i32)
// - ilogb(0) = maxInt(i32)
// - ilogb(nan) = maxInt(i32)
const std = @import("../index.zig");
const math = std.math;
const assert = std.debug.assert;
const maxInt = std.math.maxInt;
const minInt = std.math.minInt;
pub fn ilogb(x: var) i32 {
const T = @typeOf(x);
return switch (T) {
f32 => ilogb32(x),
f64 => ilogb64(x),
else => @compileError("ilogb not implemented for " ++ @typeName(T)),
};
}
// NOTE: Should these be exposed publicly?
const fp_ilogbnan = -1 - 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;
}
test "math.ilogb" {
assert(ilogb(f32(0.2)) == ilogb32(0.2));
assert(ilogb(f64(0.2)) == ilogb64(0.2));
}
test "math.ilogb32" {
assert(ilogb32(0.0) == fp_ilogb0);
assert(ilogb32(0.5) == -1);
assert(ilogb32(0.8923) == -1);
assert(ilogb32(10.0) == 3);
assert(ilogb32(-123984) == 16);
assert(ilogb32(2398.23) == 11);
}
test "math.ilogb64" {
assert(ilogb64(0.0) == fp_ilogb0);
assert(ilogb64(0.5) == -1);
assert(ilogb64(0.8923) == -1);
assert(ilogb64(10.0) == 3);
assert(ilogb64(-123984) == 16);
assert(ilogb64(2398.23) == 11);
}
test "math.ilogb32.special" {
assert(ilogb32(math.inf(f32)) == maxInt(i32));
assert(ilogb32(-math.inf(f32)) == maxInt(i32));
assert(ilogb32(0.0) == minInt(i32));
assert(ilogb32(math.nan(f32)) == maxInt(i32));
}
test "math.ilogb64.special" {
assert(ilogb64(math.inf(f64)) == maxInt(i32));
assert(ilogb64(-math.inf(f64)) == maxInt(i32));
assert(ilogb64(0.0) == minInt(i32));
assert(ilogb64(math.nan(f64)) == maxInt(i32));
}
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