158 lines
4.0 KiB
C
158 lines
4.0 KiB
C
/*
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emitBranch_6502.c -- Routines to deal with code generation for
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branches and jumps in the Macross assembler (6502
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version).
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Chip Morningstar -- Lucasfilm Ltd.
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23-April-1985
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*/
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#include "macrossTypes.h"
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#include "macrossGlobals.h"
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/* emitRelativeBranch emits a relative branch instruction for the 6502,
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branching from the current location given a condition to branch upon and a
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target address. */
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void
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emitRelativeBranch(condition, target, fixupLocation)
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conditionType condition;
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valueType *target;
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valueType fixupLocation[COMPOUND_BRANCH_MAX];
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{
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int i;
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#define COMPOUND 0x00
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#define BPL_OPCODE 0x10
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#define BMI_OPCODE 0x30
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#define BVC_OPCODE 0x50
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#define BVS_OPCODE 0x70
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#define BCC_OPCODE 0x90
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#define BCS_OPCODE 0xB0
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#define BNE_OPCODE 0xD0
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#define NOP_OPCODE 0xEA
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#define BEQ_OPCODE 0xF0
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static byte conditionalBranchOpcodes[] = {
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/* CARRY_COND */ BCS_OPCODE,
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/* ZERO_COND */ BEQ_OPCODE,
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/* NEGATIVE_COND */ BMI_OPCODE,
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/* OVERFLOW_COND */ BVS_OPCODE,
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/* LT_COND */ BCC_OPCODE,
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/* LEQ_COND */ COMPOUND,
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/* SLT_COND */ COMPOUND,
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/* SLEQ_COND */ COMPOUND,
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/* ALWAYS_COND */ NOP_OPCODE,
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/* NOT_CARRY_COND */ BCC_OPCODE,
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/* NOT_ZERO_COND */ BNE_OPCODE,
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/* NOT_NEGATIVE_COND */ BPL_OPCODE,
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/* NOT_OVERFLOW_COND */ BVC_OPCODE,
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/* GEQ_COND */ BCS_OPCODE,
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/* GT_COND */ COMPOUND,
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/* SGEQ_COND */ COMPOUND,
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/* SGT_COND */ COMPOUND,
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/* NEVER_COND */ NOP_OPCODE
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};
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#define conditionalFixup(n) if (fixupLocation != NULL) \
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fixupLocation[n] = currentLocationCounter; \
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emitRelativeByteOffset(target);
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if (fixupLocation != NULL)
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for (i=0; i<COMPOUND_BRANCH_MAX; i++)
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fixupLocation[i].value = -1;
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if (conditionalBranchOpcodes[(int)condition] != COMPOUND) {
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emitByte(conditionalBranchOpcodes[(int)condition]);
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conditionalFixup(0);
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} else switch (condition) {
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case GT_COND:
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emitByte(BEQ_OPCODE); emitByte(2);
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emitByte(BCS_OPCODE); conditionalFixup(0);
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break;
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case LEQ_COND:
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emitByte(BCC_OPCODE); conditionalFixup(0);
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emitByte(BEQ_OPCODE); conditionalFixup(1);
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break;
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case SGEQ_COND:
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emitByte(BVS_OPCODE); emitByte(4);
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emitByte(BPL_OPCODE); conditionalFixup(0);
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emitByte(BMI_OPCODE); emitByte(2);
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emitByte(BMI_OPCODE); conditionalFixup(1);
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break;
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case SGT_COND:
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emitByte(BEQ_OPCODE); emitByte(8);
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emitByte(BVS_OPCODE); emitByte(4);
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emitByte(BPL_OPCODE); conditionalFixup(0);
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emitByte(BMI_OPCODE); emitByte(2);
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emitByte(BMI_OPCODE); conditionalFixup(1);
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break;
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case SLEQ_COND:
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emitByte(BEQ_OPCODE); conditionalFixup(0);
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emitByte(BVS_OPCODE); emitByte(4);
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emitByte(BMI_OPCODE); conditionalFixup(1);
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emitByte(BPL_OPCODE); emitByte(2);
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emitByte(BPL_OPCODE); conditionalFixup(2);
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break;
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case SLT_COND:
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emitByte(BVS_OPCODE); emitByte(4);
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emitByte(BMI_OPCODE); conditionalFixup(0);
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emitByte(BPL_OPCODE); emitByte(2);
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emitByte(BPL_OPCODE); conditionalFixup(1);
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break;
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default:
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botch("non-compound condition leaked thru!\n");
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break;
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}
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}
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/* emitJump emits a 6502 jump instruction given the target address */
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simpleFixupListType *
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emitJump(target, previousFixups)
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valueType *target;
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simpleFixupListType *previousFixups;
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{
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simpleFixupListType *result;
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valueType picFixup[COMPOUND_BRANCH_MAX];
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simpleFixupListType *buildSimpleFixupList();
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#define JUMP_OPCODE 0x4C
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result = previousFixups;
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if (positionIndependentCodeMode) {
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if (target == NULL) {
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emitRelativeBranch(CARRY_COND, NULL, picFixup);
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result = buildSimpleFixupList(picFixup[0], result);
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emitRelativeBranch(NOT_CARRY_COND, NULL, picFixup);
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result = buildSimpleFixupList(picFixup[0], result);
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} else {
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emitRelativeBranch(CARRY_COND, target, NULL);
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emitRelativeBranch(NOT_CARRY_COND, target, NULL);
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}
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} else {
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emitByte(JUMP_OPCODE);
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if (target == NULL) {
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result = buildSimpleFixupList(currentLocationCounter,
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result);
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emitWord(0);
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} else {
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if (target->kindOfValue != ABSOLUTE_VALUE)
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noteAnonymousReference();
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emitWordValue(target);
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}
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}
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return(result);
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}
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