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.) ; ;Clear the upper nibble of the one's digit mov W, #$0f and ascii2, W ;Multiply the tens digit by 10. mov W, <<ascii1 ;2*tens ;Note that the carry is also cleared because ;ascii1 is an ASCII number between 0x30-0x39 and W, #$1e ;Clear upper nibble of tens digit ;In addition, we clear the shifted in carry mov ascii1, W ;W = ascii1 = 2*original ascii1 rl ascii1 ;ascii1 = 4*original ascii1 rl ascii1 ;ascii1 = 8*original ascii1 add W, ascii1 ;W = 2*original ascii1 + 8 *original ascii1 ; = 10*original ascii1 ;add the one's digit add W, ascii2 ; ; Or use this one that preserves input: mov W, <<tens and W, #$1e ;w=2*tens mov temp, W rl temp ;temp=4*tens rl temp ;temp=8*tens add temp, W ;temp=8*tens+2*tens=10*tens mov W, #-'0' ;convert one's digit from ASCII to decimal add W, ones ;w=ones add W, temp ;w=ones+10*tens ;Dmitry Kiryashov [zews at AHA.RU] says: ;Destructive way to save one more clock ;-) mov W, tens ;*1 w=0x30..0x39 add tens, W ;*2 tens=0x60..0x72 rl tens ;*4 tens=0xC0..0xE4 add tens, W ;*5 tens=0xF0..0x1ED mov W, #(-11*'0') & $FF ;low byte of -48*11 add W, ones add W, tens ;add two times tens=5*original_tens add W, tens ;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 ;)
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<A HREF="http://www.sxlist.com/techref/scenix/lib/math/radix/a2b-2d8b-sd_sx.htm"> SX Microcontroller Radix Math Method ASCII decimal to Binary</A>
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