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base:8bit_multiplication_16bit_product_fast_no_tables

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base:8bit_multiplication_16bit_product_fast_no_tables [2020-08-30 01:44]
djmips
base:8bit_multiplication_16bit_product_fast_no_tables [2020-08-30 02:00] (current)
djmips
Line 7: Line 7:
 ; by djmips  ; by djmips 
 ; ;
-; inputs are mul1 and mul2 and should be zero page. +; inputs are mul1 and X.  mul1 and mul2 should be zp locations
 ; A should be zero entering but if you want it will factor in as 1/2 A added to the result. ; A should be zero entering but if you want it will factor in as 1/2 A added to the result.
 ; ;
Line 19: Line 19:
  
 MUL: MUL:
-     dec mul2 ; decrement mul2 because we will be adding with carry set for speed (an extra one)+     cpx #$00 
 +     beq zro 
 +     dex          ; decrement mul2 because we will be adding with carry set for speed (an extra one) 
 +     stx mul2
      ror mul1      ror mul1
      bcc b1      bcc b1
Line 55: Line 58:
      inc mul2      inc mul2
      rts      rts
 +     
 +zro: stx mul1
 +     tax
 +     rts     
 </code> </code>
  
  
base/8bit_multiplication_16bit_product_fast_no_tables.txt · Last modified: 2020-08-30 02:00 by djmips