I'm looking to optimize this function:
// Add signed to unsigned using saturation, return unsigned
uint8_t addwsat(uint8_t a, int8_t b) {
if(b>=0) {
if(a>255-b) return 255;
}
else {
if(a<(-b)) return 0;
}
return a+b;
}
which the compilers converts to:
uint8_t addwsat(uint8_t a, int8_t b) {
MOV R23,R24 Copy register
MOV R20,R24 Copy register
LDI R21,0x00 Load immediate
MOV R18,R22 Copy register
CLR R19 Clear Register
SBRC R18,7 Skip if bit in register cleared
LAT R19 Load and Toggle
if(b>=0) {
SBRC R22,7 Skip if bit in register cleared
RJMP PC+0x000A Relative jump
if(a>255-b) return 255;
SER R24 Set Register
LDI R25,0x00 Load immediate
SUB R24,R18 Subtract without carry
SBC R25,R19 Subtract with carry
CP R24,R20 Compare
CPC R25,R21 Compare with carry
BRGE PC+0x0C Branch if greater or equal, signed
SER R24 Set Register
RET Subroutine return
if(a<(-b)) return 0;
CLR R24 Clear Register
CLR R25 Clear Register
SUB R24,R18 Subtract without carry
SBC R25,R19 Subtract with carry
CP R20,R24 Compare
CPC R21,R25 Compare with carry
BRGE PC+0x03 Branch if greater or equal, signed
LDI R24,0x00 Load immediate
RET Subroutine return
return a+b;
MOV R24,R22 Copy register
ADD R24,R23 Add without carry
}
RET Subroutine return
I'm convinced that there is a more optimum way to achieve the same result. Any suggestions?
