11 files changed, 244 insertions, 0 deletions
diff --git a/2/3_int_arith/212.c b/2/3_int_arith/212.c
new file mode 100644
index 0000000..e746216
--- /dev/null
+++ b/2/3_int_arith/212.c
@@ -0,0 +1,36 @@
+#include <stdio.h>
+
+int bis(int x, int m) {
+    return x | m;
+}
+int bic(int x, int m) {
+    return x & ~m;
+}
+int bool_or(int x, int y) {
+    int result = bis(x, y);
+    return result;
+}
+int bool_xor(int x, int y) {
+    int result = bis(bic(x, y), bic(y, x));
+    return result;
+}
+int bool_eq(int x, int y) {
+    int result = !(x^y);
+    return result;
+}
+
+void main() {
+    printf("=== 2.11 ===\n");
+    int x = 0x87654321;
+    printf("%x\n", x & 0xFF);
+    printf("%x\n", ~x ^ 0xFF);
+    printf("%x\n", x | 0xFF);
+
+    printf("=== 2.12 ===\n");
+    printf("%x\n", bool_or(1, 1));
+    printf("%x\n", bool_xor(1, 1));
+
+    printf("=== 2.15 ===\n");
+    printf("%x\n", bool_eq(0x87654321, 0x87654321));
+    printf("%x\n", bool_eq(14, 13));
+}
diff --git a/2/3_int_arith/225.c b/2/3_int_arith/225.c
new file mode 100644
index 0000000..51f1937
--- /dev/null
+++ b/2/3_int_arith/225.c
@@ -0,0 +1,20 @@
+#include <stdio.h>
+#include <limits.h>
+
+float sum_elements(float a[], unsigned length) {
+    int i;
+    float result = 0;
+        
+    for (i = 0; i <= length-1; i++) {
+        printf("iter\n");
+        result += a[i];
+    }
+    return result;
+}
+
+void main() {
+  printf("hi\n");
+  float ele[] = {1.0, 2.0};
+  // sum_elements(ele, 0);
+  printf("%d", INT_MAX+1);
+}
diff --git a/2/3_int_arith/227.c b/2/3_int_arith/227.c
new file mode 100644
index 0000000..cc22cf9
--- /dev/null
+++ b/2/3_int_arith/227.c
@@ -0,0 +1,20 @@
+#include <stdio.h>
+#include <limits.h>
+
+// with limits.h
+int uadd_ok(unsigned x, unsigned y) {
+    printf("x: %u, y: %u\n", x, y);
+    return x <= (UINT_MAX - y);
+}
+
+// without limits.h
+int uadd_ok_without(unsigned x, unsigned y) {
+    unsigned sum = x + y;
+    return sum >= x;
+}
+
+void main() {
+    printf("%u\n", UINT_MAX);
+    printf("%d\n", uadd_ok(10, 20));
+    printf("%d", uadd_ok(UINT_MAX / 2, UINT_MAX / 2));
+}
diff --git a/2/3_int_arith/230.c b/2/3_int_arith/230.c
new file mode 100644
index 0000000..8bba282
--- /dev/null
+++ b/2/3_int_arith/230.c
@@ -0,0 +1,25 @@
+#include <limits.h>
+#include <stdio.h>
+
+int tadd_ok(int x, int y) {
+    int positive_overflow = x > 0 && y > 0 && x + y < 0;
+    int negative_overflow = x < 0 && y < 0 && x + y >= 0;
+    return !positive_overflow && !negative_overflow;
+}
+
+int tadd_buggy(int x, int y) {
+    int sum = x+y;
+    printf("sum: %d, sum-x: %d, sum-y: %d", sum, sum-x, sum-y);
+    return (sum-x == y) && (sum-y == x);
+}
+
+/* buggy */
+int tsub_ok(int x, int y) {
+    return tadd_ok(x, -y);
+}
+
+void main() {
+    printf("INT_MIN: %d, %d\n", -(INT_MIN), INT_MIN);
+    printf("result:  %d\n", tadd_ok(10, 100));
+    printf("result2: %d", tadd_buggy(INT_MAX, 1)); // The sum is a very negative number, when we take the difference with it's parts it just does a negative overflow to get the original parts back.
+} 
diff --git a/2/3_int_arith/236.c b/2/3_int_arith/236.c
new file mode 100644
index 0000000..b05da34
--- /dev/null
+++ b/2/3_int_arith/236.c
@@ -0,0 +1,19 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <inttypes.h>
+
+int tmult_ok(int x, int y) {
+    int64_t upcasted_result = (int64_t) x * y;
+    return upcasted_result == (int) upcasted_result;
+}
+
+void main() {
+    int m = 1<<31;
+    int n = 1<<31;
+    printf("%" PRId64 "\n", (int64_t) (m * n));
+    printf("%d\n", tmult_ok(m, n));
+    printf("%d\n", tmult_ok(10, 20));
+    printf("%d\n", tmult_ok(10, 20));
+}
+
+
diff --git a/2/3_int_arith/242.c b/2/3_int_arith/242.c
new file mode 100644
index 0000000..07634e3
--- /dev/null
+++ b/2/3_int_arith/242.c
@@ -0,0 +1,14 @@
+#include <stdio.h>
+
+int div16(int x) {
+    // my inefficient method that just checks the sign bit: int sign_bit = (unsigned) (x & 1<<31) >> 31;
+    int bias = (x >> 31) & 0xF;
+    return (x + bias)>>4;
+}
+
+void main() {
+    int result = div16(-17);
+    printf("%d\n", result);
+    result = div16(17);
+    printf("%d\n", result);
+}
diff --git a/2/3_int_arith/243.c b/2/3_int_arith/243.c
new file mode 100644
index 0000000..9a60eda
--- /dev/null
+++ b/2/3_int_arith/243.c
@@ -0,0 +1,22 @@
+// #define M
+// #define K
+// int arith(int x, int y) {
+//     int result = 0;
+//     result = x*M + y/N;
+//     return result;
+// }
+//
+// int optarith(int x, int y) {
+//     int t = x;
+//     x <<= 5;
+//     x -= t;
+//     if (y < 0) y += 7;
+//     y >>= 3;
+//     return x+y;
+// }
+#include <stdio.h>
+
+int main() {
+    int x = 3;
+    printf("%d", x<<1);
+}
diff --git a/2/3_int_arith/check b/2/3_int_arith/check
new file mode 100755
index 0000000..f50a240
--- /dev/null
+++ b/2/3_int_arith/check
diff --git a/2/3_int_arith/check-211.c b/2/3_int_arith/check-211.c
new file mode 100644
index 0000000..174b0f4
--- /dev/null
+++ b/2/3_int_arith/check-211.c
@@ -0,0 +1,27 @@
+#include <stdio.h>
+
+void inplace_swap(int *x, int *y) {
+    *y = *x ^ *y;
+    *x = *x ^ *y;
+    *y = *x ^ *y;
+}
+
+void reverse_array(int a[], int cnt) {
+    int first, last;
+    for (first = 0, last = cnt-1;
+         first < last;
+         first++,last--)
+        inplace_swap(&a[first], &a[last]);
+}
+
+void print_array(int a[], int len) {
+    int i;
+    for (i = 0; i < len; i++)
+        printf("%d", a[i]);
+}
+
+void main() {
+    int a[] = {1,2,3,4,5, 6};
+    reverse_array(a, 6);
+    print_array(a, 6);
+}
diff --git a/2/3_int_arith/show-bytes.c b/2/3_int_arith/show-bytes.c
new file mode 100644
index 0000000..0860b8d
--- /dev/null
+++ b/2/3_int_arith/show-bytes.c
@@ -0,0 +1,33 @@
+#include <stdio.h>
+
+typedef unsigned char *byte_pointer;
+
+void show_bytes(byte_pointer start, size_t len) {
+    int i;
+    for (i = 0; i < len; i++)
+        printf(" %.2x", start[i]);
+    printf("\n");
+}
+
+void show_int(int x) {
+    show_bytes((byte_pointer) &x, sizeof(int));
+}
+
+
+void show_float(float x) {
+    show_bytes((byte_pointer) &x, sizeof(float));
+}
+
+
+void show_pointer(void *x) {
+    show_bytes((byte_pointer) &x, sizeof(void *));
+}
+
+void test_show_bytes(int val) {
+    int ival = val;
+    float fval = (float) ival;
+    int *pval = &ival;
+    show_int(ival);
+    show_float(fval);
+    show_pointer(pval);
+}
diff --git a/2/3_int_arith/xdr.c b/2/3_int_arith/xdr.c
new file mode 100644
index 0000000..63d4b24
--- /dev/null
+++ b/2/3_int_arith/xdr.c
@@ -0,0 +1,28 @@
+#include <stdio.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+
+void* copy_elements(void* ele_src[], int ele_cnt, size_t ele_size)  {
+    uint64_t asize = ele_cnt * (uint64_t) ele_size;
+    void *result = malloc(asize);
+    if (result == NULL)
+	return NULL;
+    void *next = result;
+    int i;
+    for (i = 0; i < ele_cnt; i++) {
+	memcpy(next, ele_src[i], ele_size);
+	next += ele_size;
+    }
+    return result;
+}
+
+void main() {
+    int i = 0;
+    char* input[] = {"somestring","some666666"};
+    printf("%s\n", input[0]);
+    printf("%s\n", *(input+1)); // these two lines are basically the same thing *(input+1) = input[1]
+    char* result = copy_elements((void *) input, 2, 10);
+    printf("%s\n", result);
+}