[INSTRUCTIONS]

You are a program-analysis assistant. Perform a **static** data-dependence analysis on a given code snippet, treating each branch or loop condition as potentially taking any outcome, without using semantic or symbolic execution to prune paths.


## 1. Data Dependence Definition

   Data dependence captures the influence of data flow between variables.

   We denote each variable instance as `(var,lineNumber)`, meaning the variable `var` defined or updated at `lineNumber`.

   >  **Direct Data Dependence**
   A variable instance `(varB,lineB)` is **directly** data-dependent on `(varA,lineA)` if `lineA` writes to `varA`. Then, without overwritting the value of `varA`, `lineB` reads `varA` and compute the value of `varB`. In other words, the value of `(varB,lineB)` relies on the value produced at `(varA,lineA)`. In addition, changing the execution order of `(varA,lineA)` and `(varB,lineB)` would alter their results.


   A variable instance `(varB,lineB)` is data-dependent on `(varA,lineA)` if there is a **transitive** (indirect) chain of **direct** data dependencies from `(varA,lineA)` to `(varB,lineB)`. This is equivalent to saying that `(varA,lineA)` has data dependence over `(varB,lineB)`, meaning the value written at `(varA,lineA)` can propagate to `(varB,lineB)` through a sequence of read/write operations.


## 2. Output Format
   When asked "Does `(varA,lineA)` have data dependence over `(varB,lineB)`? If so, provide one feasible trace.": 
   - If data dependence exists, respond:
   ```json
   {
   "DataDependence": true,
   "Trace": [
      { "from": ["varA", lineA], "to": ["varX", lineX] },
      ...
      { "from": ["varY", lineY], "to": ["varB", lineB] }
      ]
   }
   ```

   -  If no data dependence exists, respond:
   ```json
   {
   "DataDependence": false
   }
   ```
   
   A **trace** represents a **transitive data flow**, where each item represents a **direct** data dependence edge. The full trace should begin with `(varA,lineA)` and end with `(varB,lineB)`.

   You only need to provide **one** valid chain of data dependence if you conclude a data dependence exists, even if multiple possible chains exist. 


## 3. Intraprocedural Data Dependence
   All dependence analysis is performed within **a single function**. We do not track dependencies across function boundaries. The analysis only applies to variables and control structures inside the **specified function**.

## 4. Example Code Snippet

### Example 1

```python
1    total = 0
2    value = 1
3    step = value
4    if step > 1:
5        value += 3
6    while total <= 10:
7        total += value
8        difference = total - step
9        step += 1
10   final_result = total * 2
```


#### Example Question 1.1:
Does `(value,2)` have data dependence over `(step,9)`? If so, provide a trace.

**Analysis**:
- Line 9: `step += 1`, meaning `(step,9)` is directly data-dependent on `(step,3)` (or `(step,9)` itself) because step is updated based on its previous value.
- Line 3: `step = value`, meaning `(step,3)` is directly data-dependent on `(value,2)`.
Therefore, there exists a transitive data dependence chain from `(value,2)` to `(step,9)` through `(step,3)`.


**Output**:
```json
{
  "DataDependence": true,
  "Trace": [
    { "from": ["value", 2], "to": ["step", 3] },
    { "from": ["step", 3], "to": ["step", 9] }
  ]
}
```

#### Example Question 1.2 
Does `(value,2)` have data dependence over `(total,7)`? If so, provide a trace.

**Analysis**:
- Line 7: `total += value`, meaning `(total,7)` reads `value` from either `(value,2)` or `(value,5)`.
- Line 5: `value` is updated in `value += 3`, meaning `(value,5)` depends on `(value,2)` (or `(value,5)` itself). However, this update is inside an if statement, which means it may or may not execute depending on runtime conditions.
- Line 2: value is initialized at `(value,2)`.


At this point, whether `(total,7)` depends on `(value,5)` depends on whether line 4 (`if step>1`) is `true`. Since this is a static analysis, all possible paths are considered without analyzing actual reachability. This means line 5 is treated as both possibly executed and possibly not executed.

- If line 4 evaluates to `true`, `(total,7)` depends on `(value,5)`, forming the trace: `(value,2) -> (value,5) -> (total,7)`. 
- If line 4 evaluates to `false`, `(total,7)` directly depends on `(value,2)`, forming the trace: `(value,2) -> (total,7)`

Therefore, the answer is yes.
Only one valid trace is required for the output. 

**Output**:
```json
{
  "DataDependence": true,
  "Trace": [
    { "from": ["value", 2], "to": ["value", 5] },
    { "from": ["value", 5], "to": ["total", 7] }
  ]
}

```



#### Example Question 1.3
Does `(step,3)` have data dependence over `(final_result,10)`? If so, provide a trace.  

**Analysis**:
Since there is no direct or transitive data dependence between `(step,3)` and `(final_result,10)`, the answer is No.

**Output**:
```json
{
  "DataDependence": false
}
```

**Analysis**:


### Example 2

```python
1    arr = [1, 2, 3]
2    x = 5
3    if x > 2:
4        arr[0] = x   
5    for i in range(3):
6        arr[i] += 1  
7        temp = arr[i]  
8        y = temp + 1  
9    result = arr[-1]
```

#### Example Question 2.1:
Does `(x,2)` have data dependence over `(arr,6)`? If so, provide a trace.

**Analysis**
- Line 6: `arr[i] += 1` modifies `arr[i]`, but i varies during the loop execution.
   - If `i == 0`, `arr[i]` refers to `arr[0]`, which was updated in line 4 (or line 6 itself), establishing a dependence chain `(arr,4)` -> `(arr,6)`.
   - If `i != 0`, `arr[i]` does not refer to `arr[0]`, meaning it depend on `(arr,1)` (or `(arr,6)` itself), not `(arr,4)`.
   - However, since static analysis considers all possible paths without resolving i’s runtime value, we must assume `arr[i]` could be `arr[0]`, leading to a possible dependence.
- Line 4: `arr[0] = x`, meaning `(arr,4)` depends on `(x,2)`.
- Line 2: `x` is initialized at `(x,2)`.
- Since there is a transitive chain of direct data dependence: `(x,2)->(arr,4)->(arr,6)`, the answer is yes.


**Output**:
```json
{
  "DataDependence": true,
  "Trace": [
    { "from": ["x", 2], "to": ["arr", 4] },
    { "from": ["arr", 4], "to": ["arr", 6] }
  ]
}
```


#### Example Question 2.2:
Does `(i,5)` have data dependence over `(temp,7)`? If so, provide a trace.

**Analysis**:
- Line 7: `temp = arr[i]`, meaning temp depends on `i`, since `i` determines which element of arr is accessed.
- Line 5: `i` is initialized and iterates over the range 0 to 3.
- Since there is a transitive chain of direct data dependence: `(i,5)->(temp,7)`, the answer is yes.


**Output**:
```json
{
  "DataDependence": true,
  "Trace": [
    { "from": ["i", 5], "to": ["temp", 7] }
  ]
}
```

#### Example Question 2.3:
Does `(i,5)` have data dependence over `(result,9)`? If so, provide a trace.

**Analysis**:
- Line 9: `result = arr[-1]`, meaning result depends on `arr[-1]`, which is arr[2], possibly get updated at line 6 (or line 1).
- Line 6: `arr[i] += 1`, meaning `arr[i]` is modified based on the value of `i`.
- Line 5: `i` iterates over 0 to 3.
- Since there is a transitive chain of direct data dependence: `(i,5)->(arr,6)->(result,9)`, the answer is yes.


**Output**:
```json
{
  "DataDependence": true,
  "Trace": [
    { "from": ["i", 5], "to": ["arr", 6] },
    { "from": ["arr", 6], "to": ["result", 9] }
  ]
}
```

---

[YOUR TURN]

Below is **your target snippet**. 

```C
1   #include <stdio.h>
2   #include <stdlib.h>
3   #include <string.h>
4   #include <math.h>
5   int descending_compare(const void *a, const void *b){
6       if (*(int*)a > *(int*)b){
7           return -1;
8       }else if (*(int*)a == *(int*)b){
9           return 0;
10      }else{
11          return 1;
12      }
13  }
14  int ascending_compare(const void *a, const void *b){
15      if (*(int*)a < *(int*)b){
16          return -1;
17      }else if (*(int*)a == *(int*)b){
18          return 0;
19      }else{
20          return 1;
21      }
22  }
23  int lower_bound(int *a, int n, int key){
24      int left, mid, right;
25      left = 0, right = n;
26      mid = (left + right)/2;
27      while ((left+1 != mid || mid+1 != right) && mid != left){
28          if (key > a[mid]){
29              left = mid;
30          }else{
31              right = mid+1;
32          }
33          mid = (left + right)/2;
34      }
35      if (a[left] >= key)return left;
36      if (a[mid] >= key)return mid;
37      if (a[right] >= key)return right;
38      return n;
39  }
40  unsigned long  gcd(unsigned long x, unsigned long y){
41      if (y == 0){ 
42          return x;
43      }else if (x > y){
44          return gcd(y, x % y);
45      }else{
46          return gcd(x, y % x);
47      }
48  }
49  long long factorial(int x){
50      long long rtn = 1;
51      int i;
52      for (i = x; i > 1; i--){
53          rtn = (rtn*i);
54      }
55      return rtn;
56  }
57  int main(void){
58      int h, w;
59      long long square[3];
60      long long min, max;
61      long long ans = 10000000000000;
62      scanf("%d %d", &h, &w);
63      for (int i = 1; i < h; i++){
64          square[0] = (long long)i * w;
65          square[1] = (long long)(h-i)*(w/2);
66          square[2] = (long long)(h-i)*(w-w/2);
67          min = 10000000000000, max = 0;
68          for (int j = 0; j < 3; j++){
69              if (min > square[j]){
70                  min = square[j];
71              }
72              if (max < square[j]){
73                  max = square[j];
74              }
75          }
76          if (ans > llabs(max-min)){
77              ans = llabs(max-min);
78          }
79          square[1] = (long long)(h-i)/2*w;
80          square[2] = (long long)((h-i)-(h-i)/2)*w;
81          min = 10000000000000, max = 0;
82          for (int j = 0; j < 3; j++){
83              if (min > square[j]){
84                  min = (long long)square[j];
85              }
86              if (max < square[j]){
87                  max = (long long)square[j];
88              }
89          }
90          if (ans > llabs(max-min)){
91              ans = llabs(max-min);
92          }
93      }
94      for (int i = 0; i < w; i++){
95          square[0] = (long long)i*h;
96          square[1] = (long long)(w-i)*(h/2);
97          square[2] = (long long)(w-i)*(h-h/2);
98          min = 10000000000000, max = 0;
99          for (int j = 0; j < 3; j++){
100              if (min > square[j]){
101                  min = (long long)square[j];
102              }
103              if (max < square[j]){
104                  max = (long long)square[j];
105              }
106          }
107          if (ans > llabs(max-min)){
108              ans = llabs(max-min);
109          }
110          square[1] = (long long)(w-i)/2*h;
111          square[2] = (long long)((w-i)-(w-i)/2)*h;
112          min = 10000000000000, max = 0;
113          for (int j = 0; j < 3; j++){
114              if (min > square[j]){
115                  min = (long long)square[j];
116              }
117              if (max < square[j]){
118                  max = (long long)square[j];
119              }
120          }
121          if (ans > llabs(max-min)){
122              ans = llabs(max-min);
123          }
124      }
125      printf("%lld\n", ans);
126      return 0;
127  }
```


**Question**: Does `(square,79)` have data dependence over `(ans,91)` in function `main`? If so, provide a trace.

**Output**:


Ground truth answer: yes