/*When I was a kid with a Commodore 64,
the 6502 chip had no multiply inst
and this is how we had to do it, except,
I used more regs in this example.
*/
asm {
//Opcodes are slightly different to make writing my x86_64 assembler easier.
//See $LK,"::/Compiler/OpCodes.DD"$.

//You can clobber RAX,RBX,RCX,RDX,R8,R9.	The compiler expects that.

MUL_BY_HAND_U8_U8_TO_U16: //This is only for fun.
//8bit * 8bit-->16bit
//AL*BL-->AX
				MOV 		CL, 8
				SHL 		AX, 8
@@05: 			SHL1		AX
				JNC 		@@10
				ADD 		AL, BL
@@10: 			DEC 		CL
				JNZ 		@@05
				RET

_MUL_BY_HAND_U8_U8_TO_U16:: 		//C callable
				PUSH		RBP
				MOV 		RBP, RSP
				MOV 		AL,  U8 SF_ARG1[RBP] //$LK,"SF_ARG1",A="FF:::/Kernel/KernelA.HH,SF_ARG1"$
				MOV 		BL,  U8 SF_ARG2[RBP]
				CALL		MUL_BY_HAND_U8_U8_TO_U16
				MOVZX 		RAX, AX
				POP 		RBP
				RET1		16

_MUL_U64_U64_TO_U128::
//64bit * 64bit-->128bit
				PUSH		RBP
				MOV 		RBP, RSP
				MOV 		RBX, U64 SF_ARG3[RBP]
				MOV 		RAX, U64 SF_ARG1[RBP] //$LK,"SF_ARG1",A="FF:::/Kernel/KernelA.HH,SF_ARG1"$
				MUL 		U64 SF_ARG2[RBP]	//Res RDX:RAX 128bit
				MOV 		U64 [RBX], RAX
				MOV 		U64 8[RBX], RDX
				POP 		RBP
				RET1		24
};

//My convention is to put an underscore
//on C callable asm routines.
_extern _MUL_BY_HAND_U8_U8_TO_U16 U16 MulU8(U8 n1, U8 n2);

class U128
{
	U64 lo, hi;
};

_extern _MUL_U64_U64_TO_U128 U0 MulU64(I64 n1, I64 n2, U128 *_prod);

U0 MulByHand()
{
	U128 p;

	"2*7   =0x%X\n", MulU8(2, 7);
	"100*10=0x%X\n", MulU8(100, 10);

	MulU64(0x0123456789ABCDEF, 0x1000001, &p);
	"0x0123466789ABCDEF*0x1000001=0x%016X%016X\n", p.hi, p.lo;
}

MulByHand;

