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80 lines
1.9 KiB
80 lines
1.9 KiB
/*[
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sub.c
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LOCAL CHAR SccsID[]="@(#)sub.c 1.5 02/09/94";
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SUB CPU functions.
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------------------
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]*/
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#include <insignia.h>
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#include <host_def.h>
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#include <xt.h>
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#include <c_main.h>
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#include <c_addr.h>
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#include <c_bsic.h>
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#include <c_prot.h>
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#include <c_seg.h>
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#include <c_stack.h>
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#include <c_xcptn.h>
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#include <c_reg.h>
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#include <sub.h>
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/*
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=====================================================================
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EXTERNAL FUNCTIONS START HERE.
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=====================================================================
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*/
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/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
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/* Generic - one size fits all 'sub'. */
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/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
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GLOBAL VOID
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SUB
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IFN3(
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IU32 *, pop1, /* pntr to dst/lsrc operand */
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IU32, op2, /* rsrc operand */
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IUM8, op_sz /* 8, 16 or 32-bit */
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)
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{
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IU32 result;
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IU32 carry;
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IU32 msb;
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IU32 op1_msb;
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IU32 op2_msb;
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IU32 res_msb;
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msb = SZ2MSB(op_sz);
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result = *pop1 - op2 & SZ2MASK(op_sz); /* Do operation */
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op1_msb = (*pop1 & msb) != 0; /* Isolate all msb's */
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op2_msb = (op2 & msb) != 0;
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res_msb = (result & msb) != 0;
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carry = *pop1 ^ op2 ^ result; /* Isolate carries */
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/* Determine flags */
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/*
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OF = (op1 == !op2) & (op1 ^ res)
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ie if operand signs differ and res sign different to original
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destination set OF.
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*/
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SET_OF((op1_msb != op2_msb) & (op1_msb ^ res_msb));
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/*
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Formally:- CF = !op1 & op2 | res & !op1 | res & op2
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Equivalently:- CF = OF ^ op1 ^ op2 ^ res
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*/
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SET_CF(((carry & msb) != 0) ^ GET_OF());
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SET_PF(pf_table[result & BYTE_MASK]);
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SET_ZF(result == 0);
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SET_SF((result & msb) != 0); /* SF = MSB */
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SET_AF((carry & BIT4_MASK) != 0); /* AF = Bit 4 carry */
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*pop1 = result; /* Return answer */
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}
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