circ shift

CMakeLists.txt

@@ -12,6 +12,7 @@ add_executable( arrToBin                src/arrToBin.c              )
 add_executable( ascii                   src/ascii.c                 ) 
 add_executable( calculator              src/calculator.c            ) 
 add_executable( callreference           src/callreference.c         ) 
+add_executable( circular_shift          src/circular_shift.c        ) 
 add_executable( complex                 src/complex.c               ) 
 add_executable( dividableBy7            src/dividableBy7.c          ) 
 add_executable( structdump              src/structdump.c            ) 

src/circular_shift.c

@@ -0,0 +1,36 @@
+/**
+ * C implementation for bit rotating:
+ * see https://en.wikipedia.org/wiki/Circular_shift#Implementing_circular_shifts
+ */
+
+
+/*
+ * Shift operations in C are only defined for shift values which are
+ * not negative and smaller than sizeof(value) * CHAR_BIT.
+ * The mask, used with bitwise-and (&), prevents undefined behaviour
+ * when the shift count is 0 or >= the width of unsigned int.
+ */
+
+#include <stdint.h>  // for uint32_t, to get 32-bit-wide rotates, regardless of the size of int.
+#include <limits.h>  // for CHAR_BIT
+
+uint32_t rotl32 (uint32_t value, unsigned int count) {
+    const unsigned int mask = CHAR_BIT * sizeof(value) - 1;
+    count &= mask;
+    return (value << count) | (value >> (-count & mask));
+}
+
+uint32_t rotr32 (uint32_t value, unsigned int count) {
+    const unsigned int mask = CHAR_BIT * sizeof(value) - 1;
+    count &= mask;
+    return (value >> count) | (value << (-count & mask));
+}
+
+uint32_t main() {
+    uint32_t x = 0x1337;
+    uint32_t rotr = rotr32(x, 17);
+    uint32_t rotl = rotl32(x, 17);
+    printf("original:\t%032b - 0x%x - %d\n", x, x, x, x);
+    printf("rshifted:\t%032b - 0x%x - %d\n", x, rotr, rotr, rotr);
+    printf("lshifted:\t%032b - 0x%x - %d\n", x, rotl, rotl, rotl);
+}