1.20. ARRAYS
.xword .LC11
.xword .LC12
.xword .LC13
.LC2:
.string "January"
.LC3:
.string "February"
.LC4:
.string "March"
.LC5:
.string "April"
.LC6:
.string "May"
.LC7:
.string "June"
.LC8:
.string "July"
.LC9:
.string "August"
.LC10:
.string "September"
.LC11:
.string "October"
.LC12:
.string "November"
.LC13:
.string "December"
The address of the table is loaded in X1 usingADRP/ADDpair.
Then corresponding element is picked using just oneLDR, which takes W0 (the register where input argu-
mentmonthis), shifts it 3 bits to the left (which is the same as multiplying by 8), sign-extends it (this is
what “sxtw” suffix implies) and adds to X0. Then the 64-bit value is loaded from the table into X0.
MIPS
Listing 1.238: Optimizing GCC 4.4.5 (IDA)get_month1:
; load address of table into $v0:
la $v0, month1
; take input value and multiply it by 4:
sll $a0, 2
; sum up address of table and multiplied value:
addu $a0, $v0
; load table element at this address into $v0:
lw $v0, 0($a0)
; return
jr $ra
or $at, $zero ; branch delay slot, NOP
.data # .data.rel.local
.globl month1
month1: .word aJanuary # "January"
.word aFebruary # "February"
.word aMarch # "March"
.word aApril # "April"
.word aMay # "May"
.word aJune # "June"
.word aJuly # "July"
.word aAugust # "August"
.word aSeptember # "September"
.word aOctober # "October"
.word aNovember # "November"
.word aDecember # "December"
.data # .rodata.str1.4
aJanuary: .ascii "January"<0>
aFebruary: .ascii "February"<0>