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base:short_8bit_multiplication_16bit_product

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. No tables required.

FAC1     = $58
FAC2     = $59

        ; A*256 + X = FAC1 * FAC2
MUL8
        lda #$00
        ldx #$08
        clc
m0      bcc m1
        clc
        adc FAC2
m1      ror
        ror FAC1
        dex
        bpl m0
        ldx FAC1
        rts
base/short_8bit_multiplication_16bit_product.txt · Last modified: 2015-10-20 07:02 by graham