Getting Started with M68K Coral 66: Compilation System for the Motorola M68000 Family
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B.7. Opcodes

B.7.1. Branch Improvement

Certain pseudo opcodes are permitted for branch instructions. They expand to the shortest branch instructions that reach the target. Generally these mnemonics are made by substituting j for b at the start of a Motorola mnemonic.

The following table summarizes the pseudo-operations.

Table B-1. Assembler Pseudo Operations

	Displacement
Pseudo-Op	BYTE	WORD	68020 LONG	68000/10 LONG	non-PC relative
jbsr	bsr	bsrw	bsrl	jsr	jsr
jra	bras	bra	bral	jmp	jmp
j`XX`[a]	b`XX`s	b`XX`	b`XX`l	b`NX`s; jmpl	b`NX`s; jmp
db`XX`[a]	db`XX`s	db`XX`	db`XX`; bra; jmpl
fj`XX`[a]	fb`XX`w	fb`XX`w	fb`XX`l	N/A	fb`NX`w; jmp
Notes: a. XX: condition, NX: negative of condition, see full description below.

jbsr, jra

These are the simplest jump pseudo-operations; they always map to one particular machine instruction, depending on the displacement to the branch target.

jXX

Here, jXX stands for an entire family of pseudo-operations, where XX is a conditional branch or condition-code test. The full list of pseudo-ops in this family is:

jhi	jls	jcc	jcs	jne	jeq	jvc	jvs
jpl	jmi	jge	jlt	jgt	jle

For the cases of non-PC relative displacements and long displacements on the 68000 or 68010, the Assembler issues a longer code fragment in terms of NX, the opposite condition to XX. For example, for the non-PC relative case:

        jXX foo

gives

        bNXs .L1
        jmp foo
.L1:

dbXX

The full family of pseudo-operations covered here is:

dbhi	dbls	dbcc	dbcs	dbne	dbeq	dbvc	dbvs
dbpl	dbmi	dbge	dblt	dbgt	dble	dbf	dbra
dbt

Other than for word and byte displacements, when the source reads dbXX foo, the Assembler emits

        dbXX .L1
        bra .L2
.L1:    jmpl foo
.L2:

fjXX

This family includes the following:

fjne	fjeq	fjge	fjlt	fjgt	fjle	fjf	fjt
fjgl	fjgle	fjnge	fjngl	fjngle	fjngt	fjnle	fjnlt
fjoge	fjogl	fjogt	fjole	fjolt	fjor	fjseq	fjsf
fjsne	fjst	fjueq	fjuge	fjugt	fjule	fjult	fjun

For branch targets that are not PC relative, the Assembler emits:

        fbNX .L1
        jmp foo
.L1:

when it encounters fjXX foo.

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