scale8_video()

LIB8STATIC_ALWAYS_INLINE uint8_t scale8_video	(	uint8_t	i,
		fract8	scale )

The "video" version of scale8() guarantees that the output will be only be zero if one or both of the inputs are zero.

If both inputs are non-zero, the output is guaranteed to be non-zero. This makes for better "video"/LED dimming, at the cost of several additional cycles.

Parameters

i	input value to scale
scale	scale factor, in n/256 units

Returns

scaled value

See also

scale8()

Definition at line 117 of file scale8.h.

                                                                       {
#if SCALE8_C == 1 || defined(LIB8_ATTINY)
    uint8_t j = (((int)i * (int)scale) >> 8) + ((i && scale) ? 1 : 0);
    // uint8_t nonzeroscale = (scale != 0) ? 1 : 0;
    // uint8_t j = (i == 0) ? 0 : (((int)i * (int)(scale) ) >> 8) +
    // nonzeroscale;
    return j;
#elif SCALE8_AVRASM == 1
    uint8_t j = 0;
    asm volatile("  tst %[i]\n\t"
                 "  breq L_%=\n\t"
                 "  mul %[i], %[scale]\n\t"
                 "  mov %[j], r1\n\t"
                 "  clr __zero_reg__\n\t"
                 "  cpse %[scale], r1\n\t"
                 "  subi %[j], 0xFF\n\t"
                 "L_%=: \n\t"
                 : [j] "+d"(j) // r16-r31, restricted by subi
                 : [i] "r"(i), [scale] "r"(scale)
                 : "r0", "r1");
    return j;
    // uint8_t nonzeroscale = (scale != 0) ? 1 : 0;
    // asm volatile(
    //      "      tst %0           \n"
    //      "      breq L_%=        \n"
    //      "      mul %0, %1       \n"
    //      "      mov %0, r1       \n"
    //      "      add %0, %2       \n"
    //      "      clr __zero_reg__ \n"
    //      "L_%=:                  \n"
    //      : "+a" (i)
    //      : "a" (scale), "a" (nonzeroscale)
    //      : "r0", "r1");
    // // Return the result
    // return i;
#else
#error "No implementation for scale8_video available."
#endif
}

References LIB8STATIC_ALWAYS_INLINE, and scale.

Referenced by brighten8_video(), ColorFromPalette(), ColorFromPalette(), ColorFromPalette(), dim8_video(), HeatColor(), and hsv2rgb_rainbow().

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