Finished exercises 2-7 and 2-8

2020-10-18 17:15:40 -04:00
parent 987de46e0c
commit 8a8707cc35
3 changed files with 163 additions and 0 deletions
@@ -0,0 +1,41 @@
+/*
+ * Simple implementation of getbits() function.
+ *
+ */
+
+#include <stdio.h>
+
+
+// Gets n bits from position p
+unsigned getbits(unsigned int x, int p, int n);
+
+int main()
+{
+    // 11111110111 = 1015
+    unsigned int x = 1015;
+    int p = 4;
+    int n = 3;
+
+    // Result is 111 = 7
+    unsigned int some_bits = getbits(x, p, n);
+
+
+    return 0;
+}
+
+
+unsigned getbits(unsigned int x, int p, int n)
+{
+    printf("(%d >> (%d + 1 - %d)) & ~(~0 << %d)\n", x, p, n, n);
+    printf("(%d >> (%d + 1 - %d)) & ~(%d << %d)\n", x, p, n, ~0, n);
+    printf("(%d >> (%d + 1 - %d)) & ~(%d)\n", x, p, n, ((~0) << n));
+    printf("(%d >> (%d + 1 - %d)) & %d\n", x, p, n, ~((~0) << n));
+    printf("(%d >> %d) & %d\n", x, (p + 1 - n), ~((~0) << n));
+    printf("%d & %d\n", (x >> (p + 1 - n)), ~((~0) << n));
+    printf("%d\n", ((x >> (p + 1 - n)) & ~((~0) << n)));
+    // At position 4 and 3 bits from that position of value 1023 is
+    // 11111110111 = 1015
+    //      110    = 6
+
+    return (x >> (p + 1 - n)) & ~(~0 << n);
+}