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Use when the algorithm pads a 2D array with sentinel border values and uses nested initialization loops with per-cell conditionals to set them, creating extra symbolic branches per cell
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Basado en la clasificación ocupacional SOC
| name | avoid-redundant-bounds-sentinels |
| description | Use when the algorithm pads a 2D array with sentinel border values and uses nested initialization loops with per-cell conditionals to set them, creating extra symbolic branches per cell |
A KLEE-coverage code transformation. Applying it rewrites C source so symbolic execution explores more of the program's behavior.
When the algorithm pads a 2D array with sentinel border values and uses nested initialization loops with per-cell conditionals to set them, creating extra symbolic branches per cell
Replace the padded sentinel array with a tight n×n array and use natural loop bounds (x>=0 && x<n) for boundary detection, initializing all cells uniformly without per-cell branching
KLEE forks on every conditional inside initialization loops; uniform initialization plus arithmetic bound checks collapse many symbolic branches into fewer, simpler path conditions, letting the solver reach the algorithm's interesting logic faster
Before:
#include <stdio.h>
#define N 100
int main(void){
int dx[] = {0,1,0,-1};
int dy[] = {-1,0,1,0};
int map[N+2][N+2];
int datas,d,dd,n;
int x,y;
scanf("%d", &datas);
for (int i=0; i<datas; i++){
// get size
scanf("%d", &n);
// reset map
for (int xx=0; xx<n+2; xx++){
for (int yy=0; yy<n+2; yy++){
if (xx==0 || xx==n+1 || yy==0 || yy==n+1){
map[xx][yy]=-1;
}else {
map[xx][yy]=0;
}
}
}
x=1; y=n; d=0; dd=1;
// set spiral
while(1){
map[x][y]=1;
if (map[x+dx[d]][y+dy[d]]==0){
map[x+dx[dd]][y+dy[dd]]=-1;
} else{
if (map[x+dx[dd]][y+dy[dd]]==-1){
break;
}else{
d = (d+1)%4;
dd = (dd+1)%4;
}
}
x += dx[d];
y += dy[d];
}
// output
for (int yy=1; yy<=n; yy++){
for (int xx=1; xx<=n; xx++){
printf(map[xx][yy]==1?"#":" ");
}
printf("\n");
}
if (i<datas-1) printf("\n");
}
return 0;
}
After:
#include<stdio.h>
int main()
{
const int N = 100;
char a[N][N];
int n,d,caseCount=0,i,j,x,y,dd[]={-1,0,1,0},angle,c;
scanf("%d",&d);
while(d--)
{
scanf("%d",&n);
for(i=0;i<n;++i)for(j=0;j<n;++j)a[i][j]=' ';
x=0;y=n-1;
angle=0;
for(c=0;c<3;++c)
{
for(;x>=0&&y>=0&&x<n&&y<n; x+=dd[(angle+1)%4],y+=dd[angle])
{
a[y][x]='#';
}
x-=dd[(angle+1)%4];
y-=dd[angle];
angle=(angle+1)%4;;
}
if(n>2)
{
for(;n;)
{
c=0;
for(; a[y+2*dd[angle]][x+2*dd[(angle+1)%4]]!='#'; x+=dd[(angle+1)%4],y+=dd[angle])
a[y][x]='#',c++;
if(c<2) break;
angle=(angle+1)%4;;
}
a[y][x]='#';
}
else if(n==2)
a[n-1][n-1]=' ';
printf("%s",(caseCount++?"\n":""));
for(i=0;i<n;++i)
{
for(j=0;j<n;++j)
putchar(a[i][j]);
putchar('\n');
}
}
return 0;
}
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