From: Scott Dattalo
Translated and optimized for the Scenix SX by Nikolai Golovchenko
;****************************************** ;bcd_sub ; ; Computes x = x - y ; where x and y are all 8-bit packed BCD numbers ; Exits with C=0 if x<y, and with z=1 if x-y = 0 ; ; Size: 14 instructions ; Execution time including return: 14/15 cycles bcd_sub mov W, y ;x = x - y sub x, W clr W sb DC ;if lsn of x < lsn of y (dec) or W, #$06 ;then substract extra 6 snb C ;Similarly for the msn jmp bcd_sub2 or W, #$60 sub x, W ;correct result clrb C ;restore carry ret bcd_sub2 sub x, W ;correct result setb C ;restore carry ret
With result in a different register:
;****************************************** ;bcd_sub_to ; ; Computes s = x - y ; where x and y are all 8-bit packed BCD numbers ; Exits with C=0 if x<y, and with z=1 if x-y = 0 ; ; Size: 15 instructions ; Execution time including return: 15/16 cycles bcd_sub_to mov W, y ;x = x - y mov W, x-W mov s, W clr W sb DC ;if lsn of x < lsn of y (dec) or W, #$06 ;then substract extra 6 snb C ;Similarly for the msn jmp bcd_sub_to2 or W, #$60 sub s, W ;correct result clrb C ;restore carry ret bcd_sub_to2 sub s, W ;correct result setb C ;restore carry ret
file: /Techref/scenix/lib/math/sub/bcdp2_sx.htm, 1KB, , updated: 2004/6/10 14:40, local time: 2024/8/22 05:29,
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