exp2_fp()

static FASTLED_FORCE_INLINE s8x24 fl::s8x24::exp2_fp ( s8x24 x )

inlinestaticprivate

Definition at line 353 of file s8x24.h.

                                                                   {
        s8x24 fl_val = floor(x);
        s8x24 fr = x - fl_val;
        i32 n = fl_val.mValue >> FRAC_BITS;
        if (n >= INT_BITS - 1) return from_raw(0x7FFFFFFF);
        if (n < -FRAC_BITS) return s8x24();
        i32 int_pow;
        if (n >= 0) {
            int_pow = static_cast<i32>(SCALE) << n;
        } else {
            int_pow = static_cast<i32>(SCALE) >> (-n);
        }
        // 4-term minimax coefficients for 2^t - 1, t in [0,1).
        // Stored as i64 with 24 fractional bits (same as FRAC_BITS).
        constexpr int IFRAC = 24;
        constexpr i64 d0 = 11629376LL;  // 0.69316 * 2^24
        constexpr i64 d1 = 4038400LL;   // 0.24071 * 2^24
        constexpr i64 d2 = 895232LL;    // 0.05336 * 2^24
        constexpr i64 d3 = 214016LL;    // 0.01276 * 2^24
        // fr is already at 24 frac bits (same as FRAC_BITS).
        i64 fr24 = static_cast<i64>(fr.mValue);
        // Horner: 1 + fr * (d0 + fr * (d1 + fr * (d2 + fr * d3)))
        i64 acc = d3;
        acc = d2 + ((acc * fr24) >> IFRAC);
        acc = d1 + ((acc * fr24) >> IFRAC);
        acc = d0 + ((acc * fr24) >> IFRAC);
        constexpr i64 one24 = 1LL << IFRAC;
        i64 frac_pow24 = one24 + ((acc * fr24) >> IFRAC);
        // Scale by int_pow (result stays at 24 frac bits).
        i64 result =
            (static_cast<i64>(int_pow) * frac_pow24) >> FRAC_BITS;
        return from_raw(static_cast<i32>(result));
    }

References s8x24(), FASTLED_FORCE_INLINE, FL_NOEXCEPT, floor(), FRAC_BITS, from_raw(), INT_BITS, mValue, SCALE, and fl::x.

Referenced by pow().

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