no way to compare when less than two revisions

Differences

This shows you the differences between two versions of the page.

@@ Line 1: / Line 1: @@
+====== Short 8bit * 8bit = 16bit multiply ======
+A small multiplication routine using the ancient egyptian multiplication algorithm. Factors should be stored in the FAC1 and FAC2 variables, the product can be found in Akku (high byte) and the X-Register (low byte). FAC1 will be destroyed. FAC2 is modified to FAC2-1. No tables required. Mod by djmips to increase performance but increased by one byte in size. There is an unwound version of this posted separately.
+<code>
+FAC1     = $58
+FAC2     = $59
+        ; A*256 + X = FAC1 * FAC2
+MUL8
+        lda #$00
+        ldx #$08
+        dec FAC2  ; FAC2-1
+        clc
+m0      bcc m1
+        adc FAC2  ; +FAC2-1 + 1 (carry)
+m1      ror
+        ror FAC1
+        dex
+        bpl m0
+        ldx FAC1
+        rts
+</code>