Multiply 16 bits by 16 bits in software by http://elm-chan.org/
;-----------------------------------------------------------------------------: ; 16bit x 16bit unsigned multiply ; ; Register Variables ; Call: var1[1:0] = 16bit multiplicand ; var1[3:2] = <don't care> ; var2[1:0] = 16bit multiplier ; lc = <don't care> (high register must be allocated) ; ; Result:var1[3:0] = 32bit result of var1[1:0] * var2[1:0] ; var2[1:0] = <not changed> ; lc = 0 ; ; Size = 13 words ; Clock = 157..172 cycles (+ret) ; Stack = 0 byte mul16u: sub var13,var13 ;initialize variables sub var12,var12 ; ldi lc,17 ; lc = 17; brcc PC+3 ;---- calcurating loop add var12,var20 ; adc var13,var21 ; ror var13 ; ror var12 ; ror var11 ; ror var10 ; dec lc ;if (--lc > 0) brne PC-8 ; continue loop; ret mul16s: clr lc ; Optional fast signed helper clr var12 ; process with fast unsinged routine tst var11 brpl PC+6 inc var12 com var10 com var11 adc var10,lc adc var11,lc tst var21 brpl PC+6 inc var12 com var20 com var21 adc var20,lc adc var21,lc bst var12,0 rcall mul16u brtc PC+9 com var10 com var11 com var12 com var13 adc var10,lc adc var11,lc adc var12,lc adc var13,lc ret
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