Posted on November 11, 2017 at 23:27 Are there optimized basic math functions available for the STM8 such as; 8 bit by 8 bit multiply and 8 bit by 16 bit multiply and similar?
My application has a time critical 8 bit by 16 bit multiply. The Cosmic compiler seems to always default to a 16 bit by 16 bit multiply, which is slower.I wrote an inline assembly macro that runs in about 2/3 the time of the compiler's output; but it was very tedious to write. I would rather not do this for every math function.
Any helpful information would be appreciated.
I include my macro here, in case anyone else finds it useful:
// macro to perform an optimized UI8 by UI16 multiply: uint16_t
RESULT_UI16 = (uint8_t)X_UI8 * (uint16_t)Y_UI16;
// Note: All arguments must be declared '@tiny'
// macro assumes that no overflow occurs
// '_asm()' will load an 8 bit argument in reg A or a 16 argument into reg X
#define MULT_8x16(X_UI8, Y_UI16, RESULT_UI16) {\
_asm('LDW Y,X\n SWAPW X\n',(uint16_t)Y_UI16);\
_asm('MUL X,A\n SWAPW X\n PUSHW X\n LDW X,Y\n', (uint8_t)X_UI8);\
_asm('MUL X,A\n ADDW X,($1,SP)\n POPW Y\n');\
_asm('CLRW Y\n LD YL,A\n LDW (Y),X\n',(@tiny uint16_t*)(&RESULT_UI16));\
}
#compiler #math
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