Scott Dattalo and Dmitry Kiryashov

;ascii1 and ascii2 are the tens and ones digit of a number we wish ;to convert to binary ; ; In C: ; ; binary = (ascii1 & 0xf) * 10 + (ascii2 & 0xf); ; ; (I'd be interested to see how a compiler would generate the asm for this.) ; movlw 0x0f andwf ascii2,f ;Clear the upper nibble of the one's digit ; Multiply the ones digit by 10. rlf ascii1,w ;2*tens ;Note that the carry is also cleared because ;ascii1 is an ASCII number between 0x30-0x39 andlw 0x1e ;Clear upper nibble of tens digit ;In addition, we clear the shifted in carry movwf ascii1 ;W = ascii1 = 2*original ascii1 rlf ascii1,f ;ascii1 = 4*original ascii1 rlf ascii1,f ;ascii1 = 8*original ascii1 addwf ascii1,w ;W = 2*original ascii1 + 8 *original ascii1 ; = 10*original ascii1 addwf ascii2,w ; ; Or use this one that saves a cycle: rlf tens,w andlw 0x1e ;w=2*tens movwf temp rlf temp,f ;temp=4*tens rlf temp,f ;temp=8*tens addwf ones,w addlw -'0' ;convert from ASCII to decimal ;w=tens*2 + ones addwf temp,w ;w=10*tens + ones ;Dmitry Kiryashov [zews at AHA.RU] says: ;Destructive way to save one more clock ;-) movfw tens ;*1 addwf tens,F ;*2 rlf tens,F ;*4 addwf tens,F ;*5 rlf tens,W ;*10 addwf ones,W addlw low -11.*'0' ;Why so ? tens is '0' + x , ones is '0' + y , where x and y are in range ;of 0..9 So finally '0'*(10+1)=48.*11.=528.=0x210 . it is constant so we ;can subtract it back from result. Here we gone ;)

file: /Techref/microchip/math/radix/a2b-2d8b-sd.htm, 2KB, , updated: 2002/7/30 10:45, local time: 2024/7/13 17:51, |

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