authorgravatar for hi@viri.moeviri <hi@viri.moe> 2022-04-01 15:18:02-06:00
committergravatar for mail@isaacfreund.comIsaac Freund <mail@isaacfreund.com> 2022-04-06 15:50:36+02:00
log2f6ee4a97d95fe3e0ff7418e57d05242aa5aae7d
tree22d786daa7fc9958676709730bfafc8f95227942
parent5b8ac9821dd25c3e5282130b4d93d6c5b7debb08

math.isNormal: simplify implementation, add tests

1 files changed, 43 insertions(+), 46 deletions(-)

lib/std/math/isnormal.zig+43-46
......@@ -1,57 +1,54 @@
11const std = @import("../std.zig");
22const math = std.math;
33const expect = std.testing.expect;
4const maxInt = std.math.maxInt;
54
6// Returns whether x has a normalized representation (i.e. integer part of mantissa is 1).
5/// Returns whether x is neither zero, subnormal, infinity, or NaN.
76pub fn isNormal(x: anytype) bool {
87 const T = @TypeOf(x);
9 switch (T) {
10 f16 => {
11 const bits = @bitCast(u16, x);
12 return (bits +% (1 << 10)) & (maxInt(u16) >> 1) >= (1 << 11);
13 },
14 f32 => {
15 const bits = @bitCast(u32, x);
16 return (bits +% (1 << 23)) & (maxInt(u32) >> 1) >= (1 << 24);
17 },
18 f64 => {
19 const bits = @bitCast(u64, x);
20 return (bits +% (1 << 52)) & (maxInt(u64) >> 1) >= (1 << 53);
21 },
22 f128 => {
23 const bits = @bitCast(u128, x);
24 return (bits +% (1 << 112)) & (maxInt(u128) >> 1) >= (1 << 113);
25 },
26 else => {
27 @compileError("isNormal not implemented for " ++ @typeName(T));
28 },
8 const TBits = std.meta.Int(.unsigned, @bitSizeOf(T));
9 if (@typeInfo(T) != .Float) {
10 @compileError("isNormal not implemented for " ++ @typeName(T));
2911 }
12
13 const increment_exp = 1 << math.floatMantissaBits(T);
14 const remove_sign = ~@as(TBits, 0) >> 1;
15
16 // We add 1 to the exponent, and if it overflows to 0 or becomes 1,
17 // then it was all zeroes (subnormal) or all ones (special, inf/nan).
18 // The sign bit is removed because all ones would overflow into it.
19 // For f80, even though it has an explicit integer part stored,
20 // the exponent effectively takes priority if mismatching.
21 const value = @bitCast(TBits, x) +% increment_exp;
22 return value & remove_sign >= (increment_exp << 1);
3023}
3124
3225test "math.isNormal" {
33 try expect(!isNormal(math.nan(f16)));
34 try expect(!isNormal(math.nan(f32)));
35 try expect(!isNormal(math.nan(f64)));
36 try expect(!isNormal(math.nan(f128)));
37 try expect(!isNormal(-math.nan(f16)));
38 try expect(!isNormal(-math.nan(f32)));
39 try expect(!isNormal(-math.nan(f64)));
40 try expect(!isNormal(-math.nan(f128)));
41 try expect(!isNormal(math.inf(f16)));
42 try expect(!isNormal(math.inf(f32)));
43 try expect(!isNormal(math.inf(f64)));
44 try expect(!isNormal(math.inf(f128)));
45 try expect(!isNormal(-math.inf(f16)));
46 try expect(!isNormal(-math.inf(f32)));
47 try expect(!isNormal(-math.inf(f64)));
48 try expect(!isNormal(-math.inf(f128)));
49 try expect(!isNormal(@as(f16, 0)));
50 try expect(!isNormal(@as(f32, 0)));
51 try expect(!isNormal(@as(f64, 0)));
52 try expect(!isNormal(@as(f128, 0)));
53 try expect(isNormal(@as(f16, 1.0)));
54 try expect(isNormal(@as(f32, 1.0)));
55 try expect(isNormal(@as(f64, 1.0)));
56 try expect(isNormal(@as(f128, 1.0)));
26 // TODO remove when #11391 is resolved
27 if (@import("builtin").os.tag == .freebsd) return error.SkipZigTest;
28
29 // TODO add `c_longdouble' when math.inf(T) supports it
30 inline for ([_]type{ f16, f32, f64, f80, f128 }) |T| {
31 const TBits = std.meta.Int(.unsigned, @bitSizeOf(T));
32
33 // normals
34 try expect(isNormal(@as(T, 1.0)));
35 try expect(isNormal(math.floatMin(T)));
36 try expect(isNormal(math.floatMax(T)));
37
38 // subnormals
39 try expect(!isNormal(@as(T, -0.0)));
40 try expect(!isNormal(@as(T, 0.0)));
41 try expect(!isNormal(@as(T, math.floatTrueMin(T))));
42
43 // largest subnormal
44 try expect(!isNormal(@bitCast(T, ~(~@as(TBits, 0) << math.floatMantissaDigits(T) - 1))));
45
46 // non-finite numbers
47 try expect(!isNormal(-math.inf(T)));
48 try expect(!isNormal(math.inf(T)));
49 try expect(!isNormal(math.nan(T)));
50
51 // overflow edge-case (described in implementation, also see #10133)
52 try expect(!isNormal(@bitCast(T, ~@as(TBits, 0))));
53 }
5754}