base:short_8bit_multiplication_16bit_product
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| base:short_8bit_multiplication_16bit_product [2020-08-29 23:12] – djmips | base:short_8bit_multiplication_16bit_product [2020-08-30 01:52] (current) – old revision restored (2015-10-20 07:02) djmips | ||
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| ====== Short 8bit * 8bit = 16bit multiply ====== | ====== 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. | + | 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. |
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| lda #$00 | lda #$00 | ||
| ldx #$08 | ldx #$08 | ||
| - | dec FAC2 ; FAC2-1 | ||
| clc | clc | ||
| m0 bcc m1 | m0 bcc m1 | ||
| - | adc FAC2 ; this is just + FAC2 because FAC2-1 plus the set carry = FAC2 | + | |
| + | | ||
| m1 ror | m1 ror | ||
| ror FAC1 | ror FAC1 | ||
base/short_8bit_multiplication_16bit_product.1598735578.txt.gz · Last modified: 2020-08-29 23:12 by djmips