1.22. MANIPULATING SPECIFIC BIT(S)
These instructions are used for resetting (BTR), setting (BTS) and inverting (or complementing:BTC) spe-
cific bits. The 31st bit isMSB, counting from 0.
Finally, the result is copied intoXMM0, because floating point values are returned throughXMM0in Win64
environment.
MIPS
GCC 4.4.5 for MIPS does mostly the same:
Listing 1.284: Optimizing GCC 4.4.5 (IDA)my_abs:
; move from coprocessor 1:
mfc1 $v1, $f12
li $v0, 0x7FFFFFFF
; $v0=0x7FFFFFFF
; do AND:
and $v0, $v1
; move to coprocessor 1:
mtc1 $v0, $f0
; return
jr $ra
or $at, $zero ; branch delay slot
set_sign:
; move from coprocessor 1:
mfc1 $v0, $f12
lui $v1, 0x8000
; $v1=0x80000000
; do OR:
or $v0, $v1, $v0
; move to coprocessor 1:
mtc1 $v0, $f0
; return
jr $ra
or $at, $zero ; branch delay slot
negate:
; move from coprocessor 1:
mfc1 $v0, $f12
lui $v1, 0x8000
; $v1=0x80000000
; do XOR:
xor $v0, $v1, $v0
; move to coprocessor 1:
mtc1 $v0, $f0
; return
jr $ra
or $at, $zero ; branch delay slot
One singleLUIinstruction is used to load 0x80000000 into a register, becauseLUIis clearing the low 16
bits and these are zeros in the constant, so oneLUIwithout subsequentORIis enough.
ARM
Optimizing Keil 6/2013 (ARM mode)
Listing 1.285: Optimizing Keil 6/2013 (ARM mode)my_abs PROC
; clear bit:
BIC r0,r0,#0x80000000
BX lr
ENDP
set_sign PROC