Intel XENIX 286 Programmers Guide (86) - Tenox.tc

XENIX Programming as: Assembler
Branch Instructions
The XENIX assembler has a new class of instructions, called branch instructions, that
test a condition and branch to an instruction address further than 128 bytes away.
These instructions take the same kind of operand as the normal jmp instruction but
provide a test to see whether or not the jump should occur. The following is a list of the
branch instructions.
beq
bge
bgt
bhi
bhis
ble
blo
blos
blt
bne
br
The branch instructions, when assembled, consist of two 8086/286 jump instructions. The
first jump tests for the inverse of the condition specified by the branch. The second
jump is the unconditional jump instruction jmp. If the branch condition is true, the first
jump is ignored and the second jump taken. If the branch condition is false, the first
jump is taken. The first jump passes control to the next statement after the second
jump.
For example, the statement
bne subtest
is equivalent to the statements
no:
je no
jmp subtest
String Instructions
The XENIX assembler uses a subset of the string instructions normally available for the
8086/286 processor. In particular, the assembler accepts only those string instructions
that do not take operands. These are essentially the byte and word forms of the string
instructions with implied destination.
To indicate this restriction, some instruction mnemonics no longer contain the "s" for
string. The following is a list of the string instructions:
cmpsb
cmps
lodb
lodw
movsb
movs
scab
scaw
stob
stow
The assembler also accepts the rep, repnz, and repz instructions for repeating string
operations. Note that these instructions must appear alone on a line; they cannot be
combined on the same line with a string instruction.
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