I did the leg-work. To me, the call_table() approach looks faster - no cmp/jumps to pass through every time, and simpler code for debugging.
--- C-code "exer.c" file containing the different techniques:
#include
int add(int first, int second);
int sub(int first, int second);
int mult(int first, int second);
int divide(int first, int second);
typedef int math_function(int first, int second);
math_function *my_array[4] = {
add,
sub,
mult,
divide
};
int add(int first, int second){
return first + second;
}
int sub(int first, int second){
return first - second;
}
int mult(int first, int second){
return first * second;
}
int divide(int first, int second){
return first / second;
}
int inline_with_switch() {
int first, second, choice, result;
first = 2;
second = 3;
choice = 1;
switch(choice) {
case 0 :
result = first + second;
break;
case 1 :
result = first - second;
break;
case 2 :
result = first * second;
break;
case 3 :
result = first / second;
break;
}
printf("Result is %d\n", result);
return 0;
}
int functions_with_switch() {
int first, second, choice, result;
first = 2;
second = 3;
choice = 1;
switch(choice) {
case 0 :
result = add(first, second);
break;
case 1 :
result = sub(first, second);
break;
case 2 :
result = mult(first, second);
break;
case 3 :
result = divide(first, second);
break;
}
printf("Result is %d\n", result);
return 0;
}
int call_table() {
int first, second, choice, result;
first = 2;
second = 3;
choice = 1;
math_function *my_array[4] = {
add,
sub,
mult,
divide
};
result = my_array[choice](first, second);
printf("Result is %d\n", result);
return 0;
}
void main(int argc, char *argv[])
{
call_table();
inline_with_switch();
functions_with_switch();
}
--- Assembly Code (produced with gcc -S exer.c -o exer.s):
.file "exer.c"
.text
.def printf; .scl 3; .type 32; .endef
.seh_proc printf
printf:
pushq %rbp
.seh_pushreg %rbp
pushq %rbx
.seh_pushreg %rbx
subq $56, %rsp
.seh_stackalloc 56
leaq 48(%rsp), %rbp
.seh_setframe %rbp, 48
.seh_endprologue
movq %rcx, 32(%rbp)
movq %rdx, 40(%rbp)
movq %r8, 48(%rbp)
movq %r9, 56(%rbp)
leaq 40(%rbp), %rax
movq %rax, -16(%rbp)
movq -16(%rbp), %rbx
movl $1, %ecx
movq __imp___acrt_iob_func(%rip), %rax
call *%rax
movq %rbx, %r8
movq 32(%rbp), %rdx
movq %rax, %rcx
call __mingw_vfprintf
movl %eax, -4(%rbp)
movl -4(%rbp), %eax
addq $56, %rsp
popq %rbx
popq %rbp
ret
.seh_endproc
.globl my_array
.data
.align 32
my_array:
.quad add
.quad sub
.quad mult
.quad divide
.text
.globl add
.def add; .scl 2; .type 32; .endef
.seh_proc add
add:
pushq %rbp
.seh_pushreg %rbp
movq %rsp, %rbp
.seh_setframe %rbp, 0
.seh_endprologue
movl %ecx, 16(%rbp)
movl %edx, 24(%rbp)
movl 16(%rbp), %edx
movl 24(%rbp), %eax
addl %edx, %eax
popq %rbp
ret
.seh_endproc
.globl sub
.def sub; .scl 2; .type 32; .endef
.seh_proc sub
sub:
pushq %rbp
.seh_pushreg %rbp
movq %rsp, %rbp
.seh_setframe %rbp, 0
.seh_endprologue
movl %ecx, 16(%rbp)
movl %edx, 24(%rbp)
movl 16(%rbp), %eax
subl 24(%rbp), %eax
popq %rbp
ret
.seh_endproc
.globl mult
.def mult; .scl 2; .type 32; .endef
.seh_proc mult
mult:
pushq %rbp
.seh_pushreg %rbp
movq %rsp, %rbp
.seh_setframe %rbp, 0
.seh_endprologue
movl %ecx, 16(%rbp)
movl %edx, 24(%rbp)
movl 16(%rbp), %eax
imull 24(%rbp), %eax
popq %rbp
ret
.seh_endproc
.globl divide
.def divide; .scl 2; .type 32; .endef
.seh_proc divide
divide:
pushq %rbp
.seh_pushreg %rbp
movq %rsp, %rbp
.seh_setframe %rbp, 0
.seh_endprologue
movl %ecx, 16(%rbp)
movl %edx, 24(%rbp)
movl 16(%rbp), %eax
cltd
idivl 24(%rbp)
popq %rbp
ret
.seh_endproc
.section .rdata,"dr"
.LC0:
.ascii "Result is %d\12\0"
.text
.globl inline_with_switch
.def inline_with_switch; .scl 2; .type 32; .endef
.seh_proc inline_with_switch
inline_with_switch: