zig/std/math/ilogb.zig
Andrew Kelley b8ed0cb374 remove workaround for LLVM not respecting "nobuiltin"
now that we depend on LLVM 5.0.0 we can remove the
workaround.

closes #393
2017-08-28 04:28:42 -04:00

130 lines
2.9 KiB
Zig

// Special Cases:
//
// - ilogb(+-inf) = @maxValue(i32)
// - ilogb(0) = @maxValue(i32)
// - ilogb(nan) = @maxValue(i32)
const math = @import("index.zig");
const assert = @import("../debug.zig").assert;
pub fn ilogb(x: var) -> i32 {
const T = @typeOf(x);
switch (T) {
f32 => @inlineCall(ilogb32, x),
f64 => @inlineCall(ilogb64, x),
else => @compileError("ilogb not implemented for " ++ @typeName(T)),
}
}
// NOTE: Should these be exposed publically?
const fp_ilogbnan = -1 - i32(@maxValue(u32) >> 1);
const fp_ilogb0 = fp_ilogbnan;
fn ilogb32(x: f32) -> i32 {
var u = @bitCast(u32, x);
var e = i32((u >> 23) & 0xFF);
// TODO: We should be able to merge this with the lower check.
if (math.isNan(x)) {
return @maxValue(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 @maxValue(i32);
}
}
e - 0x7F
}
fn ilogb64(x: f64) -> i32 {
var u = @bitCast(u64, x);
var e = i32((u >> 52) & 0x7FF);
if (math.isNan(x)) {
return @maxValue(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 @maxValue(i32);
}
}
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)) == @maxValue(i32));
assert(ilogb32(-math.inf(f32)) == @maxValue(i32));
assert(ilogb32(0.0) == @minValue(i32));
assert(ilogb32(math.nan(f32)) == @maxValue(i32));
}
test "math.ilogb64.special" {
assert(ilogb64(math.inf(f64)) == @maxValue(i32));
assert(ilogb64(-math.inf(f64)) == @maxValue(i32));
assert(ilogb64(0.0) == @minValue(i32));
assert(ilogb64(math.nan(f64)) == @maxValue(i32));
}