q16FromFloatBits()

bool fl::q16FromFloatBits	(	float	value,
		i32 *	out )

s16.16 of a float, rounded to nearest, computed from its IEEE-754 bits with integer arithmetic only – no soft-float helper on a part without an FPU (FastLED#4458).

False for NaN, infinity or |value| >= 32768.

Definition at line 292 of file device_solve.cpp.hpp.

                                                          {
    if (out == nullptr) {
        return false;
    }
    // Integer arithmetic on the IEEE-754 single-precision bits: sign, 8-bit
    // biased exponent, 23-bit mantissa. A float->int cast would be a call to
    // a soft-float helper (__aeabi_f2iz) on a part without an FPU, which is
    // exactly what the bind path must not reach (FastLED#4458).
    const u32 bits = fl::bit_cast<u32>(value);
    const bool negative = (bits >> 31) != 0;
    const i32 exponent = static_cast<i32>((bits >> 23) & 0xFFu);
    const u32 fraction = bits & 0x7FFFFFu;
    if (exponent == 0xFF) {
        return false;  // infinity or NaN
    }
    if (exponent == 0) {
        *out = 0;  // zero or subnormal: far below one s16.16 step
        return true;
    }
    // value = mantissa * 2^(exponent - 150); in s16.16 that is
    // mantissa * 2^(exponent - 134).
    const u64 mantissa = static_cast<u64>(fraction | 0x800000u);
    const i32 shift = exponent - 134;
    u64 magnitude = 0;
    if (shift >= 0) {
        if (shift > 7) {
            return false;  // |value| >= 32768: outside s16.16
        }
        magnitude = mantissa << shift;
    } else {
        const i32 right = -shift;
        if (right > 40) {
            magnitude = 0;
        } else {
            // Round to nearest, halves away from zero -- the same rounding
            // the float quantizers this replaces used.
            magnitude = (mantissa + (static_cast<u64>(1) << (right - 1))) >> right;
        }
    }
    if (magnitude > 0x7FFFFFFFull) {
        return false;
    }
    *out = negative ? -static_cast<i32>(magnitude) : static_cast<i32>(magnitude);
    return true;
}

References bit_cast(), FL_NO_EXCEPT, and type_rank< T >::value.

Referenced by fl::anonymous_namespace{chromatic_adaptation.cpp.hpp}::adaptationWhiteQ16(), buildRgbSolveMatrixQ16(), buildStreamingPipelineQ16(), buildWhiteAllocationFromSolveQ16(), fl::anonymous_namespace{source_xyz.cpp.hpp}::sourceChromaticityQ16(), and fl::anonymous_namespace{pipeline.cpp.hpp}::wideWhiteColumnQ16().

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