Add bitstream utility

libmineziper/CMakeLists.txt

@@ -5,11 +5,13 @@ set(libmineziper_STATIC_INCLUDE ${CMAKE_CURRENT_SOURCE_DIR}/include)
 set(libmineziper_SRC
 	${libmineziper_STATIC_SRC}/libmineziper.c
 	${libmineziper_STATIC_SRC}/libmineziper_zip.c
+	${libmineziper_STATIC_SRC}/libmineziper_bitstream.c
 )
 
 set(libmineziper_INCLUDE
 	${libmineziper_STATIC_INCLUDE}/libmineziper.h
 	${libmineziper_STATIC_INCLUDE}/libmineziper_zip.h
+	${libmineziper_STATIC_INCLUDE}/libmineziper_bitstream.h
 )
 
 # Create static library

libmineziper/include/libmineziper_bitstream.h

@@ -0,0 +1,20 @@
+#ifndef LIBMINEZIPER_BITSTREAM_H
+#define LIBMINEZIPER_BITSTREAM_H
+
+typedef struct bitstream
+{
+  char *data;
+  int data_size;        // size of 'data' array
+  int last_bit_offset;  // last bit in the stream
+
+  int current_data_offset;  // position in 'data', i.e.
+                            // data[current_data_offset] is current
+                            // reading/writing byte
+  int current_bit_offset;   // which bit we are currently reading/writing
+} bitstream;
+
+char get_bits(bitstream *bs, unsigned int size);
+void print_bits(int x, int size);
+unsigned int reverse(unsigned int x, unsigned int numBits);
+
+#endif

libmineziper/src/libmineziper_bitstream.c

@@ -0,0 +1,102 @@
+#include "libmineziper_bitstream.h"
+
+#include <assert.h>
+
+char get_bits(bitstream *bs, unsigned int size)
+{
+  if (size > 32)
+    return -1;
+
+  if (size == 0)
+    return 0;
+
+  int out;
+  if (bs->current_bit_offset + size <= 8)
+  {
+    int mask = (1 << size) - 1;
+    mask <<= bs->current_bit_offset;
+
+    out = bs->data[bs->current_data_offset] & mask;
+
+    bs->current_bit_offset += size;
+    if (bs->current_bit_offset == 8)
+    {
+      bs->current_bit_offset = 0;
+      bs->current_data_offset++;
+    }
+  }
+  else
+  {
+    int diff = 8 - bs->current_bit_offset;
+    out = get_bits(bs, diff);
+    out += get_bits(bs, (bs->current_bit_offset + size) % 8);
+  }
+
+  return out;
+}
+
+unsigned int reverse(unsigned int x, unsigned int numBits)
+{
+  static const unsigned char reverse8[256] = {
+      0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0, 0x10, 0x90, 0x50, 0xD0,
+      0x30, 0xB0, 0x70, 0xF0, 0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8,
+      0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8, 0x04, 0x84, 0x44, 0xC4,
+      0x24, 0xA4, 0x64, 0xE4, 0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
+      0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC, 0x1C, 0x9C, 0x5C, 0xDC,
+      0x3C, 0xBC, 0x7C, 0xFC, 0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2,
+      0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2, 0x0A, 0x8A, 0x4A, 0xCA,
+      0x2A, 0xAA, 0x6A, 0xEA, 0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
+      0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6, 0x16, 0x96, 0x56, 0xD6,
+      0x36, 0xB6, 0x76, 0xF6, 0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE,
+      0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE, 0x01, 0x81, 0x41, 0xC1,
+      0x21, 0xA1, 0x61, 0xE1, 0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
+      0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9, 0x19, 0x99, 0x59, 0xD9,
+      0x39, 0xB9, 0x79, 0xF9, 0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5,
+      0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5, 0x0D, 0x8D, 0x4D, 0xCD,
+      0x2D, 0xAD, 0x6D, 0xED, 0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
+      0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3, 0x13, 0x93, 0x53, 0xD3,
+      0x33, 0xB3, 0x73, 0xF3, 0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB,
+      0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB, 0x07, 0x87, 0x47, 0xC7,
+      0x27, 0xA7, 0x67, 0xE7, 0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
+      0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF, 0x1F, 0x9F, 0x5F, 0xDF,
+      0x3F, 0xBF, 0x7F, 0xFF};
+
+  assert(x < (unsigned int) (1 << numBits));
+
+  // fast lookup if it fits in a byte
+  if (numBits == 8)
+    return reverse8[(unsigned char) x];
+
+  if (numBits < 8)
+    return reverse8[(unsigned char) x] >> (8 - numBits);
+
+  // more than a byte, slower
+  unsigned int result = 0;
+  for (unsigned int i = 0; i < numBits; i++)
+  {
+    result <<= 1;
+    result |= x & 1;
+    x >>= 1;
+  }
+  return result;
+}
+
+int get_bit_length(int x)
+{
+  int n = 0;
+  while (x != 0)
+  {
+    x >> 1;
+    n++;
+  }
+  return n;
+}
+
+void print_bits(int x, int size)
+{
+  for (int i = size - 1; i >= 0; i--)
+  {
+    printf("%c", 0b1 & (x >> i) ? '1' : '0');
+  }
+  printf("(%d,%d)", x, size);
+}