1const std = @import("../std.zig");
2const math = std.math;
3const expect = std.testing.expect;
4
5/// Returns whether x is neither zero, subnormal, infinity, or NaN.
6pub fn isNormal(x: anytype) bool {
7 const T = @TypeOf(x);
8 const TBits = @Int(.unsigned, @typeInfo(T).float.bits);
9
10 const increment_exp = 1 << math.floatMantissaBits(T);
11 const remove_sign = ~@as(TBits, 0) >> 1;
12
13 // We add 1 to the exponent, and if it overflows to 0 or becomes 1,
14 // then it was all zeroes (subnormal) or all ones (special, inf/nan).
15 // The sign bit is removed because all ones would overflow into it.
16 // For f80, even though it has an explicit integer part stored,
17 // the exponent effectively takes priority if mismatching.
18 const value = @as(TBits, @bitCast(x)) +% increment_exp;
19 return value & remove_sign >= (increment_exp << 1);
20}
21
22test isNormal {
23 // TODO add `c_longdouble' when math.inf(T) supports it
24 inline for ([_]type{ f16, f32, f64, f80, f128 }) |T| {
25 const TBits = @Int(.unsigned, @bitSizeOf(T));
26
27 // normals
28 try expect(isNormal(@as(T, 1.0)));
29 try expect(isNormal(math.floatMin(T)));
30 try expect(isNormal(math.floatMax(T)));
31
32 // subnormals
33 try expect(!isNormal(@as(T, -0.0)));
34 try expect(!isNormal(@as(T, 0.0)));
35 try expect(!isNormal(@as(T, math.floatTrueMin(T))));
36
37 // largest subnormal
38 try expect(!isNormal(@as(T, @bitCast(~(~@as(TBits, 0) << math.floatFractionalBits(T))))));
39
40 // non-finite numbers
41 try expect(!isNormal(-math.inf(T)));
42 try expect(!isNormal(math.inf(T)));
43 try expect(!isNormal(math.nan(T)));
44
45 // overflow edge-case (described in implementation, also see #10133)
46 try expect(!isNormal(@as(T, @bitCast(~@as(TBits, 0)))));
47 }
48}