add bit (14-2)

Author: yourtion

source/bit.c

@@ -0,0 +1,114 @@
+//
+//  bit.c
+//  Algorithms - Bit operations
+//
+//  Created by YourtionGuo on 17/05/2017.
+//  Copyright © 2017 Yourtion. All rights reserved.
+//
+
+
+#include <string.h>
+
+#include "bit.h"
+
+#pragma mark - Public
+
+int bit_get(const unsigned char *bits, int pos)
+{
+  unsigned char   mask;
+  int             i;
+
+  /// 设置位获取掩码
+  mask = 0x80;
+
+  for (i = 0; i < (pos % 8); i++) {
+    mask = mask >> 1;
+  }
+
+  /// 获取位
+  return (((mask & bits[(int)(pos / 8)]) == mask) ? 1 : 0);
+}
+
+
+void bit_set(unsigned char *bits, int pos, int state)
+{
+  unsigned char   mask;
+  int             i;
+
+  /// 设置位获取掩码
+  mask = 0x80;
+
+  for (i = 0; i < (pos % 8); i++) {
+    mask = mask >> 1;
+  }
+
+  /// 设置位
+  if (state) {
+    bits[pos / 8] = bits[pos / 8] | mask;
+  } else {
+    bits[pos / 8] = bits[pos / 8] & (~mask);
+  }
+
+  return;
+}
+
+
+void bit_xor(const unsigned char *bits1, const unsigned char *bits2, unsigned char *bitsx, int size)
+{
+  int       i;
+
+  /// 按位计算两个缓存区的异或值
+
+  for (i = 0; i < size; i++) {
+
+    if (bit_get(bits1, i) != bit_get(bits2, i)) {
+      bit_set(bitsx, i, 1);
+    } else {
+      bit_set(bitsx, i, 0);
+    }
+  }
+
+  return;
+}
+
+
+
+void bit_rot_left(unsigned char *bits, int size, int count)
+{
+  int       fbit = 0, lbit, i, j;
+
+  /// 向左轮转缓冲区特定位数
+
+  if (size > 0) {
+
+    for (j = 0; j < count; j++) {
+
+      for (i = 0; i <= ((size - 1) / 8); i++) {
+
+        /// 获取即将被替换的位的值
+        lbit = bit_get(&bits[i], 0);
+
+        if (i == 0) {
+
+          /// 将第一个位保存起来
+          fbit = lbit;
+
+        } else {
+
+          /// 将前一个字节最右边的位移到当前字节的最左边
+          bit_set(&bits[i - 1], 7, lbit);
+        }
+
+        /// 将特定位向左移动
+        bits[i] = bits[i] << 1;
+      }
+
+      /// 将其最右边的位移动到首字节的最高位上
+      
+      bit_set(bits, size - 1, fbit);
+    }
+  }
+  
+  return;
+}
+