Function fast_logf_approx

src/fl/math/math.h:406–415

log (natural) - fast approximate version Uses IEEE 754 bit extraction + minimax quadratic. ~1.5% max relative error. ~5-10x faster than standard logf on embedded targets.

// Uses IEEE 754 bit extraction + minimax quadratic. ~1.5% max relative error.
// ~5-10x faster than standard logf on embedded targets.
inline float fast_logf_approx(float x) FL_NOEXCEPT {
    union { float f; u32 i; } u;
    u.f = x;
    i32 e = static_cast<i32>(u.i >> 23) - 127;
    u.i = (u.i & 0x007FFFFFu) | 0x3F800000u;
    float m = u.f;
    float t = m - 1.0f;
    float log2m = t * (1.3327635f + t * (-0.3327635f));
    return (static_cast<float>(e) + log2m) * 0.6931471805599453f;
}

// log (natural)
inline float logf(float value) FL_NOEXCEPT { return log_impl_float(value); }