diff options
| -rw-r--r-- | src/lib8tion/math8.h | 46 |
1 files changed, 35 insertions, 11 deletions
diff --git a/src/lib8tion/math8.h b/src/lib8tion/math8.h index a83b1ad2..fe355e89 100644 --- a/src/lib8tion/math8.h +++ b/src/lib8tion/math8.h @@ -495,6 +495,38 @@ LIB8STATIC uint8_t blend8( uint8_t a, uint8_t b, uint8_t amountOfB) uint16_t partial; uint8_t result; +#if (FASTLED_SCALE8_FIXED == 1) + + // with SCALE8_FIXED, the algorithm above is: + // result = A*(255-amountOfB) + A + B*(amountOfB) + B + + // however, we can rearrange that to: + // result = 256*A + B - A*amountOfB + B*amountOfB + + // 1 or 2 cycles depending on how the compiler optimises + partial = (a << 8) + b; + + // 7 cycles + asm volatile ( + " mul %[a], %[amountOfB] \n\t" + " sub %A[partial], r0 \n\t" + " sbc %B[partial], r1 \n\t" + " mul %[b], %[amountOfB] \n\t" + " add %A[partial], r0 \n\t" + " adc %B[partial], r1 \n\t" + " clr __zero_reg__ \n\t" + : [partial] "+r" (partial) + : [amountOfB] "r" (amountOfB), + [a] "r" (a), + [b] "r" (b) + : "r0", "r1" + ); + +#else + + // non-SCALE8-fixed version + + // 7 cycles asm volatile ( /* partial = b * amountOfB */ " mul %[b], %[amountOfB] \n\t" @@ -510,23 +542,15 @@ LIB8STATIC uint8_t blend8( uint8_t a, uint8_t b, uint8_t amountOfB) " adc %B[partial], r1 \n\t" " clr __zero_reg__ \n\t" - -#if (FASTLED_SCALE8_FIXED == 1) - /* partial += a */ - " add %A[partial], %[a] \n\t" - " adc %B[partial], __zero_reg__ \n\t" - - // partial += b - " add %A[partial], %[b] \n\t" - " adc %B[partial], __zero_reg__ \n\t" -#endif - + : [partial] "=r" (partial), [amountOfB] "+a" (amountOfB) : [a] "a" (a), [b] "a" (b) : "r0", "r1" ); + +#endif result = partial >> 8; |