71 lines
1.4 KiB
C++
71 lines
1.4 KiB
C++
/*
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When I was a kid with a Commodore 64,
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the 6502 chip had no multiply instruction
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and this is how we had to do it, except,
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I used more regs in this example.
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*/
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asm {
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//Opcodes are slightly different to make writing my x86_64 assembler easier.
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//See $LK-A,"::/TempleOS/Compiler/OpCodes.TXT"$.
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USE64 //Defaults to 64, but this is a good habit.
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//You can clobber RAX,RBX,RCX,RDX,R8,R9
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MUL_BY_HAND_U8_U8_TO_U16: //This is only for fun.
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//8bit * 8bit-->16bit
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//AL*BL-->AX
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MOV CL,8
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SHL AX,8
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@@05: SHL1 AX
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JNC @@10
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ADD AL,BL
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@@10: DEC CL
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JNZ @@05
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RET
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_MUL_BY_HAND_U8_U8_TO_U16:: //C callable
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ENTER 0
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MOV AL,U8 SF_ARG1[RBP] //$LK,"SF_ARG1","FF:::/TempleOS/Kernel/Adam1a.HPP,SF_ARG1"$
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MOV BL,U8 SF_ARG2[RBP]
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CALL MUL_BY_HAND_U8_U8_TO_U16
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MOVZX RAX,AX
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LEAVE
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RET1 16
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_MUL_U64_U64_TO_U128::
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//64bit * 64bit-->128bit
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ENTER 0
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MOV RBX,U64 SF_ARG3[RBP]
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MOV RAX,U64 SF_ARG1[RBP] //$LK,"SF_ARG1","FF:::/TempleOS/Kernel/Adam1a.HPP,SF_ARG1"$
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MUL U64 SF_ARG2[RBP] //Result RDX:RAX 128bit
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MOV U64 [RBX],RAX
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MOV U64 8[RBX],RDX
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LEAVE
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RET1 24
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};
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//My convention is to put an underscore
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//on C callable routines.
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_extern _MUL_BY_HAND_U8_U8_TO_U16 U16 MulU8(U8 n1,U8 n2);
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class U128
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{
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U64 lo,hi;
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};
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_extern _MUL_U64_U64_TO_U128 U0 MulU64(I64 n1,I64 n2,U128 *_prod);
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U0 MulByHand()
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{
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U128 p;
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"2*7 =0x%X\n",MulU8(2,7);
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"100*10=0x%X\n",MulU8(100,10);
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MulU64(0x0123456789ABCDEF,0x1000001,&p);
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"0x0123466789ABCDEF*0x1000001=0x%016X%016X\n",p.hi,p.lo;
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}
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MulByHand;
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