| ??? 06/28/05 07:06 Read: times |
#96077 - As Matter of Fact.... Responding to: ???'s previous message |
As a matter of fact the Keil C51 compiler generates a JUMP table for a switch statement. I tried an example for a large sequential case switch with 16 cases. The compiler made an indexable jump table like this:
MOV A,sub_sel?1640+01H
CJNE A,#010H,?C0035
?C0035:
JC $ + 5H
LJMP ?C0017
MOV DPTR,#?C0036
MOV R0,A
ADD A,R0
ADD A,R0
JMP @A+DPTR
?C0036:
LJMP ?C0018
LJMP ?C0019
LJMP ?C0020
LJMP ?C0021
LJMP ?C0022
LJMP ?C0023
LJMP ?C0024
LJMP ?C0025
LJMP ?C0026
LJMP ?C0027
LJMP ?C0028
LJMP ?C0029
LJMP ?C0030
LJMP ?C0031
LJMP ?C0032
LJMP ?C0033
; {
; SOURCE LINE # 110
; case 0:
; SOURCE LINE # 111
?C0018:
; sub_ret = sub0();
; SOURCE LINE # 112
LCALL sub0
; break;
; SOURCE LINE # 113
SJMP ?C0051
;
; case 1:
; SOURCE LINE # 115
?C0019:
; sub_ret = sub1();
; SOURCE LINE # 116
LCALL sub1
?C0037:
; break;
; SOURCE LINE # 117
SJMP ?C0051
...The compiler generated code to index the JUMP table is bog standard 8051 "JMP @A+DPTR" stuff. The switch looked like this:
int sub_sel;
int sub_ret;
sub_sel = 13;
switch(sub_sel)
{
case 0:
sub_ret = sub0();
break;
case 1:
sub_ret = sub1();
break;
case 2:
sub_ret = sub2();
break;
case 3:
sub_ret = sub3();
break;
case 4:
sub_ret = sub4();
break;
case 5:
sub_ret = sub5();
break;
case 6:
sub_ret = sub6();
break;
case 7:
sub_ret = sub7();
break;
case 8:
sub_ret = sub8();
break;
case 9:
sub_ret = sub9();
break;
case 10:
sub_ret = sub10();
break;
case 11:
sub_ret = sub11();
break;
case 12:
sub_ret = sub12();
break;
case 13:
sub_ret = sub13();
break;
case 14:
sub_ret = sub14();
break;
case 15:
sub_ret = sub15();
break;
}
Michael Karas |
| Topic | Author | Date |
| Coding a Jmp table in C | 01/01/70 00:00 | |
| Jmp Tables in C | 01/01/70 00:00 | |
| you do not | 01/01/70 00:00 | |
| Call table? | 01/01/70 00:00 | |
| Of course not! | 01/01/70 00:00 | |
| use jmp@a+dptr | 01/01/70 00:00 | |
| jmp table not in C | 01/01/70 00:00 | |
| Wrong ends of sticks? | 01/01/70 00:00 | |
| You do not control the Compiler Output | 01/01/70 00:00 | |
| You can not have your cake and eat it to | 01/01/70 00:00 | |
| Jump Table in C | 01/01/70 00:00 | |
| Call Table? (again) | 01/01/70 00:00 | |
| Call Table? (again) | 01/01/70 00:00 | |
| I never did use function pointers | 01/01/70 00:00 | |
| No pain, no gain. | 01/01/70 00:00 | |
| the overlaying | 01/01/70 00:00 | |
| There can be a gain. | 01/01/70 00:00 | |
| My 2 cents worth | 01/01/70 00:00 | |
| Incorrect | 01/01/70 00:00 | |
As Matter of Fact.... | 01/01/70 00:00 |