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--- base:decimal_to_hexadecimal_conversion [2015-04-17 04:31] – external edit 127.0.0.1
+++ base:decimal_to_hexadecimal_conversion [2016-02-14 21:59] – verz
@@ Line 44: / Line 44: @@
 hiResult:	.byte $00
 loResult:	.byte $00</code>
+By Verz:
+I made a small improvement, the idea being that a 10x multiplication can be computed as a sum of a (8x + 2x); since we're shifting the high nibble to the right, we get the 8x and 2x values in the process.
+(Note that using a loResult in page zero there are 5 bytes/cycles of improvement)
+<code>
+bcdbin
+            lda #$00        ; Init result bytes
+            ;sta loResult    ; useless
+            sta hiResult
+            lda loInput     ; Fetch ones and tens
+            tay             ; Save to Y
+            and #$f0        ; this two instructions, or use the undocumented ALR #$f0 = (and #$f0) + (lsr)
+            lsr
+            ;alr #$f0
+            sta loResult
+            lsr
+            lsr
+            adc loResult
+            sta loResult
+            tya
+            and #$0f        ; Strip the ones
+            adc loResult
+            ldx hiInput     ; Fetch the hundreds
+            beq END         ; No hundreds? Then go to end
+HUND:       clc
+            adc #$64        ; Add as many hundreds as value of X
+            bcc loop
+            inc hiResult    ; Increase high byte every passed $FF
+loop:       dex
+            bne HUND
+END:        sta loResult    ; Store low byte
+            rts
+hiInput:	.byte $00
+loInput:	.byte $01
+hiResult:	.byte $00
+loResult:	.byte $00</code>
+Here a routine to convert a single BCD byte (0-99) in A, to a binary in A:
+<code>
+BCDBIN8
+          tay
+          and            #%11110000
+          lsr
+          ;alr            #%11110000  ;  =(And #$f0)+(Lsr), to replace the two previous instructions
+          sta            pzTmp
+          lsr
+          lsr
+          adc            pzTmp
+          sta            pzTmp
+          tya
+          and            #%1111
+          adc            pzTmp
+          rts
+pzTmp .equ $02    ; $02 is a unused zeropage memory location in C64
+</code>