Convert a transition table to an x86 table in C

Question

I have this x86 assembler code and am trying to convert it to C:

.GLOBAL calculate calculate: pushl %ebp movl %esp,%ebp movl 12(%ebp),%eax movl 8(%ebp),%ecx cmpl $2,%ecx ja done jmp *operations(,%ecx,4) operation1: imull %eax,%eax jmp done operation2: negl %eax jmp done operation3: addl $0x80,%eax done: leave ret operations: .long operation1, operation2, operation3 

My question is about the jmp *operations(,%ecs,4) . I think this is a switch statement, and I know how it works in memory, but how does this translate to C? Shouldn't I have known what was on the stack in these places to write a switch for it?

This is what I have:

 int calculate(int a, int b) { if (2 > a) { return b; } switch(a) { case /* ? */: b = (b * b); break; case /* ? */: b = (b * -1); break; case /* ? */: b = (b + 128); break; } return b; } 

Answer 1

 %ecx == 0 -> operations(,%ecx,4) == operations+0 and operation1 is there %ecx == 1 -> operations(,%ecx,4) == operations+4 and operation2 is there %ecx == 2 -> operations(,%ecx,4) == operations+8 and operation3 is there 

As a result, the code should be

 int calculate(int a, int b) { if ((unsigned int)a > 2) /* ja is a comparation instruction for unsigned integers */ { return b; } switch(a) { case 0: b = (b * b); break; case 1: b = (b * -1); break; case 2: b = (b + 128); break; } return b; }