Zig 0.17.0-dev (Split by item)

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ilogbX

ilogb.ilogbX

fn ilogbX(comptime T: type, x: T) i32

File

lib/std/math/ilogb.zig:28

Code

fn ilogbX(comptime T: type, x: T) i32 {
    const typeWidth = @typeInfo(T).float.bits;
    const significandBits = math.floatMantissaBits(T);
    const exponentBits = math.floatExponentBits(T);

    const Z = @Int(.unsigned, typeWidth);

    const signBit = (@as(Z, 1) << (significandBits + exponentBits));
    const maxExponent = ((1 << exponentBits) - 1);
    const exponentBias = (maxExponent >> 1);

    const absMask = signBit - 1;

    const u = @as(Z, @bitCast(x)) & absMask;
    const e: i32 = @intCast(u >> significandBits);

    if (e == 0) {
        if (u == 0) {
            math.raiseInvalid();
            return fp_ilogb0;
        }

        // offset sign bit, exponent bits, and integer bit (if present) + bias
        const offset = 1 + exponentBits + @as(comptime_int, @intFromBool(T == f80)) - exponentBias;
        return offset - @as(i32, @intCast(@clz(u)));
    }

    if (e == maxExponent) {
        math.raiseInvalid();
        if (u > @as(Z, @bitCast(math.inf(T)))) {
            return fp_ilogbnan; // u is a NaN
        } else return maxInt(i32);
    }

    return e - exponentBias;
}