1.15. SWITCH()/CASE/DEFAULT
ARM: Optimizing Keil 6/2013 (Thumb mode)
Listing 1.155: Optimizing Keil 6/2013 (Thumb mode)000000F6 EXPORT f2
000000F6 f2
000000F6 10 B5 PUSH {R4,LR}
000000F8 03 00 MOVS R3, R0
000000FA 06 F0 69 F8 BL __ARM_common_switch8_thumb ; switch 6 cases
000000FE 05 DCB 5
000000FF 04 06 08 0A 0C 10 DCB 4, 6, 8, 0xA, 0xC, 0x10 ; jump table for switch statement
00000105 00 ALIGN 2
00000106
00000106 zero_case ; CODE XREF: f2+4
00000106 8D A0 ADR R0, aZero ; jumptable 000000FA case 0
00000108 06 E0 B loc_118
0000010A
0000010A one_case ; CODE XREF: f2+4
0000010A 8E A0 ADR R0, aOne ; jumptable 000000FA case 1
0000010C 04 E0 B loc_118
0000010E
0000010E two_case ; CODE XREF: f2+4
0000010E 8F A0 ADR R0, aTwo ; jumptable 000000FA case 2
00000110 02 E0 B loc_118
00000112
00000112 three_case ; CODE XREF: f2+4
00000112 90 A0 ADR R0, aThree ; jumptable 000000FA case 3
00000114 00 E0 B loc_118
00000116
00000116 four_case ; CODE XREF: f2+4
00000116 91 A0 ADR R0, aFour ; jumptable 000000FA case 4
00000118
00000118 loc_118 ; CODE XREF: f2+12
00000118 ; f2+16
00000118 06 F0 6A F8 BL __2printf
0000011C 10 BD POP {R4,PC}
0000011E
0000011E default_case ; CODE XREF: f2+4
0000011E 82 A0 ADR R0, aSomethingUnkno ; jumptable 000000FA default case
00000120 FA E7 B loc_118
000061D0 EXPORT __ARM_common_switch8_thumb
000061D0 __ARM_common_switch8_thumb ; CODE XREF: example6_f2+4
000061D0 78 47 BX PC
000061D2 00 00 ALIGN 4
000061D2 ; End of function ARM_common_switch8_thumb
000061D2
000061D4 32ARM_common_switch8_thumb ; CODE XREF:⤦
ÇARM_common_switch8_thumb
000061D4 01 C0 5E E5 LDRB R12, [LR,#-1]
000061D8 0C 00 53 E1 CMP R3, R12
000061DC 0C 30 DE 27 LDRCSB R3, [LR,R12]
000061E0 03 30 DE 37 LDRCCB R3, [LR,R3]
000061E4 83 C0 8E E0 ADD R12, LR, R3,LSL#1
000061E8 1C FF 2F E1 BX R12
000061E8 ; End of function 32ARM_common_switch8_thumb
One cannot be sure that all instructions in Thumb and Thumb-2 modes has the same size. It can even be
said that in these modes the instructions have variable lengths, just like in x86.
So there is a special table added that contains information about how much cases are there (not including
default-case), and an offset for each with a label to which control must be passed in the corresponding