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| -rw-r--r-- | csci5271/hw1/hw1markup.md | 43 | ||||
| -rw-r--r-- | csci5271/hw1/hw1writeup.md | 96 |
2 files changed, 96 insertions, 43 deletions
diff --git a/csci5271/hw1/hw1markup.md b/csci5271/hw1/hw1markup.md deleted file mode 100644 index a870d15..0000000 --- a/csci5271/hw1/hw1markup.md +++ /dev/null @@ -1,43 +0,0 @@ -# Homework 1 -## Q1 - -## Q2 -### A: Perl -After adding a name to the request, add a semicolon followed by the command. The semicolon is the shell command separator which allows it to parse commands. -#### Example Request -``` -"?field-name=;perl+-e+'`command`'" -``` -### B: C - -## Q3 - -## Q4 -### A -#### Mistake 1a: Potentially overloading the array -If the function is called with `to` larger than outer bound of the array, there is a buffer overflow that happens. For example, running it by default with an array of size 10 with a `to` of size 11 on gcc 11.1 causes it to crash because of stack smashing. -##### Mistake 1b: Underloading the array -If the function is called with `from` smaller than 0 will cause some values of the array to be replaced with other values from memory. It did not crash, but it is not the intended behavior. -#### Mistake 2: - -#### Mistake 3: - -### B: Same Signature -```c - void reverse_range(int *a, int from, int to) { - -``` -### C: Different Signature -```c - int* reverse_range(int arr[], int arrSize, int from, int to) { - if (from < 0 || to >= arrSize) - return NULL; - for (int i = from; i < to; i++) { - int temp = arr[i]; - arr[i] = arr[to]; - arr[to] = temp; - to--; - } - return arr; -``` -## Q5
\ No newline at end of file diff --git a/csci5271/hw1/hw1writeup.md b/csci5271/hw1/hw1writeup.md new file mode 100644 index 0000000..091f4aa --- /dev/null +++ b/csci5271/hw1/hw1writeup.md @@ -0,0 +1,96 @@ +# Homework 1 + +## Q1 + + + +## Q2 + +### A: Perl + +After adding a name to the request, add a semicolon followed by the command. The semicolon is the shell command separator which allows it to parse commands. + +#### Example Request + +``` +"?field-name=;perl+-e+'`command`'" +``` + +### B: C + +## Q3 + +## Q4 + +### A + +#### Mistake 1a: Potentially overloading the array + +If the function is called with `to` larger than outer bound of the array, there is a buffer overflow that happens. For example, running it by default with an array of size 10 with a `to` of 11 on gcc 11.1 causes it to crash because of stack smashing. + +##### Mistake 1b: Underloading the array + +If the function is called with `from` smaller than 0 will cause some values of the array to be replaced with other values from memory addresses nearby. It did not crash, but it is not the intended behavior. + +#### Mistake 2 + +a + +#### Mistake 3 + +### B: Same Signature + +```c +void reverse_range(int *a, int from, int to) { + unsigned int *p = &a[from]; + unsigned int *q = &a[to]; +/* Until the pointers move past each other: */ + while (!(p == q + 1 || p == q + 2)) { +/* Swap *p with *q, without using a temporary variable */ + *p += *q; /* *p == P + Q */ + *q = *p - *q; /* *q == P + Q - Q = P */ + *p = *p - *q; /* *p == P + Q - P = Q */ +/* Advance pointers towards each other */ + p++; + q--; + } +} + +``` + +### C: Different Signature + +```c + int* reverse_range(int arr[], int arrSize, int from, int to) { + if (from < 0 || to >= arrSize || to < from) + return NULL; + for (int i = from; i < to; i++) { + int temp = arr[i]; + arr[i] = arr[to]; + arr[to] = temp; + to--; + } + return arr; + } +``` + +## Q5 + +### A + +Start out with the binary representation of 20, 00010100. Then shift the bits to the right and toggle bit 31. Then left shift (multiply by 2) and you get 20. +2147483668 and 2 are two numbers that give 20 when multiplied. +Also works with 1073741829 and 4. + +### B + +The easiest way at first would seems like it would be to get the largest unsigned integer, divide it by 7 and add 3 to get the overflow to 20, getting back to multiplying and you get 7. The problem is that doesn't work. You get 17. +The next thing to try is doubling the integer and adding 20 to get it to overflow twice. Thankfully `0x200000014` is cleanly divisible by 7. + +`200000014*7=20` + +### C + +```c + printf("$1%.27d spear%c%.0x %.7sion %o\n", 0, 104, 962029, "evacuate", 13023); +``` |