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--- base:fastest_multiplication [2017-04-17 12:30] – repose
+++ base:fastest_multiplication [2017-04-17 13:55] – repose
@@ Line 1: / Line 1: @@
+====== Fastest 16x16 unsigned multiplication ======
+By Repose
 Requires tables or a generator routine such as [[table_generator_routine_for_fast_8_bit_mul_table]]
-Jack Asser's: 233 cycles  ref: [[seriously_fast_multiplication]]
+Jack Asser's: 233 cycles  ref: [[seriously_fast_multiplication]] \\
-Chris Jam's: 204.5  ref: http://csdb.dk/forums/?roomid=11&topicid=91766
+Chris Jam's: 204.5  ref: http://csdb.dk/forums/?roomid=11&topicid=91766 \\
-Mine: 201 zp variation: 198
+Mine: 201 zp variation: 198 \\
-Times above need to add 12 for jsr/rts
+Times above need to add 12 for jsr/rts \\
 <code>
 ;World's fastest 16x16 unsigned mult for 6502
@@ Line 35: / Line 40: @@
 z3=$83
-;not shown is a routine to make the tables
+;Example showing use
-;also you need to init the pointers' high bytes to the tables
+lda #$ff
+sta x0
+sta x1
+sta y0
+sta y1
+jsr maketables
+jsr umult16
+;result should be $fffe0001, e.g. as viewed with a typical m 0080 monitor command:
+;0080 01 00 fe ff
+makesqrtables:
+;init zp square tables pointers
+lda #>sqrlo
+sta p_sqr_lo+1
+lda #>sqrhi
+sta p_sqr_hi+1
+lda #>negsqrlo
+sta p_invsqr_lo+1
+lda #>negsqrhi
+sta p_invsqr_hi+1
+;generate sqr(x)=x^2/4
+      ldx #$00
+      txa
+      !by $c9   ; CMP #immediate - skip TYA and clear carry flag
+lb1:  tya
+      adc #$00
+ml1:  sta sqrhi,x
+      tay
+      cmp #$40
+      txa
+      ror
+ml9:  adc #$00
+      sta ml9+1
+      inx
+ml0:  sta sqrlo,x
+      bne lb1
+      inc ml0+2
+      inc ml1+2
+      clc
+      iny
+      bne lb1
+;generate negsqr(x)=(255-x)^2/4
+      ldx #$00
+      ldy #$ff
+mt1:
+      lda sqrhi+1,x
+      sta negsqrhi+$100,x
+      lda sqrhi,x
+      sta negsqrhi,y
+      lda sqrlo+1,x
+      sta negsqrlo+$100,x
+      lda sqrlo,x
+      sta negsqrlo,y
+      dey
+      inx
+      bne mt1
+      rts
 umult16:
@@ Line 132: / Line 195: @@
     z3    z2    z1    z0
 </code>