Pick up on 3.4 Switch

ch_03/exercise_03-01/main.c

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+/*
+ *
+ * Exercise 3-1. Our binary search makes two tests inside the loop, when one would
+ * suffice (at the price of more tests outside). Write a version with only one test
+ * inside the loop and measure the difference in run-time.
+ *
+ * Author: Kun Deng
+ */
+
+#include <stdio.h>
+#include <limits.h>
+#include <float.h>
+
+#define ARRAY_SIZE 99900000
+
+long v[ARRAY_SIZE];
+
+long binsearch(long x, long v[], long n);
+long binsearch_improved(long x, long v[], long n);
+
+void populate_array(const long size);
+void print_array(const long v[], long size);
+
+
+int main()
+{
+    extern long v[];
+
+    populate_array(ARRAY_SIZE);
+    // print_array(v, ARRAY_SIZE);
+    
+    long x = 901103;
+
+    printf("Starting binary search. Trying to find %ld...\n", x);
+
+    long index = binsearch(x, v, ARRAY_SIZE);
+    printf("Regular binary search complete\n");
+    long index_improved = binsearch_improved(x, v, ARRAY_SIZE);
+    printf("Improved binary search complete\n");
+
+    if (index < 0)
+    {
+        printf("%ld was not found in the array\n", x);
+
+        return -1;
+    }
+
+    printf("Binary search: Value %ld is at index %ld of the array\n", x, index);
+    printf("Binary search improved: Value %ld is at index %ld of the array\n", x, index_improved);
+
+    return 0;
+}
+
+
+long binsearch(long x, long v[], long n)
+{
+    long low, mid, high;
+
+    low = 0;
+    high = n - 1;
+
+    while (low <= high)
+    {
+        mid = (low + high) / 2;
+
+        if (x < v[mid])
+        {
+            high = mid - 1;
+        }
+        else if (x > v[mid])
+        {
+            low = mid + 1;
+        }
+        else
+        {
+            return mid;
+        }
+    }
+
+    return -1;
+}
+
+long binsearch_improved(long x, long v[], long n)
+{
+    long low, mid, high;
+    
+    low = 0;
+    high = n - 1;
+    mid = (low + high) / 2;
+
+    for (; (low <= high) && x != v[mid]; mid = (low + high) / 2)
+    {
+        if (x < v[mid])
+        {
+            high = mid - 1;
+        }
+        else
+        {
+            low = mid + 1;
+        }
+    }
+
+    if (v[mid] == x)
+    {
+        return mid;
+    }
+
+
+    return -1;
+}
+
+
+void populate_array(long size)
+{
+    extern long v[];
+    long i = 0;
+    v[i] = 1; // First element will start at 1
+
+    for (i = 1; i != size; ++i)
+    {
+        long elem = v[i];
+        v[i] = elem + (i * 2) + 1;
+    }
+}
+
+void print_array(const long v[], long size)
+{
+    printf("array is: ");
+
+    for (long i = 0; i != size; ++i)
+    {
+        printf("%ld ", v[i]);
+    }
+
+    printf("\nWith %ld elements\n", size);
+}