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math.isNormal: simplify implementation, add tests

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viri 2022-04-01 15:18:02 -06:00 committed by Isaac Freund
parent 5b8ac9821d
commit 2f6ee4a97d
1 changed files with 43 additions and 46 deletions
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89
lib/std/math/isnormal.zig
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@ -1,57 +1,54 @@
const std = @import("../std.zig");
const math = std.math;
const expect = std.testing.expect;
const maxInt = std.math.maxInt;
// Returns whether x has a normalized representation (i.e. integer part of mantissa is 1).
/// Returns whether x is neither zero, subnormal, infinity, or NaN.
pub fn isNormal(x: anytype) bool {
const T = @TypeOf(x);
switch (T) {
f16 => {
const bits = @bitCast(u16, x);
return (bits +% (1 << 10)) & (maxInt(u16) >> 1) >= (1 << 11);
},
f32 => {
const bits = @bitCast(u32, x);
return (bits +% (1 << 23)) & (maxInt(u32) >> 1) >= (1 << 24);
},
f64 => {
const bits = @bitCast(u64, x);
return (bits +% (1 << 52)) & (maxInt(u64) >> 1) >= (1 << 53);
},
f128 => {
const bits = @bitCast(u128, x);
return (bits +% (1 << 112)) & (maxInt(u128) >> 1) >= (1 << 113);
},
else => {
@compileError("isNormal not implemented for " ++ @typeName(T));
},
const TBits = std.meta.Int(.unsigned, @bitSizeOf(T));
if (@typeInfo(T) != .Float) {
@compileError("isNormal not implemented for " ++ @typeName(T));
}
const increment_exp = 1 << math.floatMantissaBits(T);
const remove_sign = ~@as(TBits, 0) >> 1;
// We add 1 to the exponent, and if it overflows to 0 or becomes 1,
// then it was all zeroes (subnormal) or all ones (special, inf/nan).
// The sign bit is removed because all ones would overflow into it.
// For f80, even though it has an explicit integer part stored,
// the exponent effectively takes priority if mismatching.
const value = @bitCast(TBits, x) +% increment_exp;
return value & remove_sign >= (increment_exp << 1);
}
test "math.isNormal" {
try expect(!isNormal(math.nan(f16)));
try expect(!isNormal(math.nan(f32)));
try expect(!isNormal(math.nan(f64)));
try expect(!isNormal(math.nan(f128)));
try expect(!isNormal(-math.nan(f16)));
try expect(!isNormal(-math.nan(f32)));
try expect(!isNormal(-math.nan(f64)));
try expect(!isNormal(-math.nan(f128)));
try expect(!isNormal(math.inf(f16)));
try expect(!isNormal(math.inf(f32)));
try expect(!isNormal(math.inf(f64)));
try expect(!isNormal(math.inf(f128)));
try expect(!isNormal(-math.inf(f16)));
try expect(!isNormal(-math.inf(f32)));
try expect(!isNormal(-math.inf(f64)));
try expect(!isNormal(-math.inf(f128)));
try expect(!isNormal(@as(f16, 0)));
try expect(!isNormal(@as(f32, 0)));
try expect(!isNormal(@as(f64, 0)));
try expect(!isNormal(@as(f128, 0)));
try expect(isNormal(@as(f16, 1.0)));
try expect(isNormal(@as(f32, 1.0)));
try expect(isNormal(@as(f64, 1.0)));
try expect(isNormal(@as(f128, 1.0)));
// TODO remove when #11391 is resolved
if (@import("builtin").os.tag == .freebsd) return error.SkipZigTest;
// TODO add `c_longdouble' when math.inf(T) supports it
inline for ([_]type{ f16, f32, f64, f80, f128 }) |T| {
const TBits = std.meta.Int(.unsigned, @bitSizeOf(T));
// normals
try expect(isNormal(@as(T, 1.0)));
try expect(isNormal(math.floatMin(T)));
try expect(isNormal(math.floatMax(T)));
// subnormals
try expect(!isNormal(@as(T, -0.0)));
try expect(!isNormal(@as(T, 0.0)));
try expect(!isNormal(@as(T, math.floatTrueMin(T))));
// largest subnormal
try expect(!isNormal(@bitCast(T, ~(~@as(TBits, 0) << math.floatMantissaDigits(T) - 1))));
// non-finite numbers
try expect(!isNormal(-math.inf(T)));
try expect(!isNormal(math.inf(T)));
try expect(!isNormal(math.nan(T)));
// overflow edge-case (described in implementation, also see #10133)
try expect(!isNormal(@bitCast(T, ~@as(TBits, 0))));
}
}