Re: help with a logic algorithm

On 04/04/2024 13:06, jak wrote:

Thiago Adams ha scritto:

I need an algorithm that finds the possible states of variables used in "ifs"
>
for instance, I need to find out possible states:
>
if (a && b){
>
   // 'a' is true
   // 'b' is true
>
}
else
{
   // 'a' maybe be true or false
   // 'b' maybe be true or false
}
>
More complex:
>
if (a && b || c){
   // 'a' maybe be true or false
   // 'b' maybe be true or false
   // 'c' maybe be true or false
}
else
{
   // 'a' maybe be true or false
   // 'b' maybe be true or false
   // 'c' maybe be true or false
}
>
I think this algorithm may already exists.. but not finding it.
Maybe something related with predicates.
>
>

 I'm not sure I understand exactly what you want to obtain,
but if I understand I can propose, to you, a simple idea:
 #include <stdio.h>
 int main()
{
     #define SFMT "a:%-5.5s b: %-5.5s c: %-5.5s\n"
     #define BIT(v, t) (v & t)
     #define TST(v) ((v) ? "true" : "false")
      unsigned char a = 1 << 0,
                   b = 1 << 1,
                   c = 1 << 2;
      for(unsigned char i = 0; i <= 7; i++)
     {
         if(BIT(i, a) && BIT(i, b) || BIT(i, c))
         {
             printf("Then: " SFMT, TST(BIT(i, a)),
                                   TST(BIT(i, b)),
                                   TST(BIT(i, c)));
         }
         else
         {
             printf("Else: " SFMT, TST(BIT(i, a)),
                                   TST(BIT(i, b)),
                                   TST(BIT(i, c)));
         }
     }
     return 0;
}
   output:
Else: a:false b: false c: false
Else: a:true  b: false c: false
Else: a:false b: true  c: false
Then: a:true  b: true  c: false
Then: a:false b: false c: true
Then: a:true  b: false c: true
Then: a:false b: true  c: true
Then: a:true  b: true  c: true
 

the algorithm is be used in flow analysis of C code.
I realized my previous approach will not work because I also need intermediate result.
for instance
if (p && p->i) {}
I need to know p is not-null after && , I cannot wait until the end of expression. The algorithm must propagate the results.
I am thinking on alternatives..