added from dvdnav's dvdread getbits() code to be used in forthcoming patch to read correctly NAV data

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@24101 b3059339-0415-0410-9bf9-f77b7e298cf2

1 files changed, 70 insertions, 0 deletions

diff --git a/dvdread/nav_read.c b/dvdread/nav_read.c
index 2dee7c1ac1..e29956dc1b 100644
--- a/dvdread/nav_read.c
+++ b/dvdread/nav_read.c
@@ -32,6 +32,76 @@
 #include "nav_read.h"
 #include "dvdread_internal.h"
 
+typedef struct {
+  uint8_t *start;
+  uint32_t byte_position;
+  uint32_t bit_position;
+  uint8_t byte;
+} getbits_state_t;
+
+static int getbits_init(getbits_state_t *state, uint8_t *start) {
+  if ((state == NULL) || (start == NULL)) return 0;
+  state->start = start;
+  state->bit_position = 0;
+  state->byte_position = 0;
+  state->byte = start[0];
+  return 1;
+}
+
+/* Non-optimized getbits. */
+/* This can easily be optimized for particular platforms. */
+static uint32_t getbits(getbits_state_t *state, uint32_t number_of_bits) {
+  uint32_t result=0;
+  uint8_t byte=0;
+  if (number_of_bits > 32) {
+    printf("Number of bits > 32 in getbits\n");
+    abort();
+  }
+
+  if ((state->bit_position) > 0) {  /* Last getbits left us in the middle of a byte. */
+    if (number_of_bits > (8-state->bit_position)) { /* this getbits will span 2 or more bytes. */
+      byte = state->byte;
+      byte = byte >> (state->bit_position);
+      result = byte;
+      number_of_bits -= (8-state->bit_position);
+      state->bit_position = 0;
+      state->byte_position++;
+      state->byte = state->start[state->byte_position];
+    } else {
+      byte=state->byte;
+      state->byte = state->byte << number_of_bits;
+      byte = byte >> (8 - number_of_bits);
+      result = byte;
+      state->bit_position += number_of_bits; /* Here it is impossible for bit_position > 8 */
+      if (state->bit_position == 8) {
+        state->bit_position = 0;
+        state->byte_position++;
+        state->byte = state->start[state->byte_position];
+      }
+      number_of_bits = 0;
+    }
+  }
+  if ((state->bit_position) == 0) {
+    while (number_of_bits > 7) {
+      result = (result << 8) + state->byte;
+      state->byte_position++;
+      state->byte = state->start[state->byte_position];
+      number_of_bits -= 8;
+    }
+    if (number_of_bits > 0) { /* number_of_bits < 8 */
+      byte = state->byte;
+      state->byte = state->byte << number_of_bits;
+      state->bit_position += number_of_bits; /* Here it is impossible for bit_position > 7 */
+      byte = byte >> (8 - number_of_bits);
+      result = (result << number_of_bits) + byte;
+      number_of_bits = 0;
+    }
+  }
+
+  return result;
+}
+
+
 void navRead_PCI(pci_t *pci, unsigned char *buffer) {
   int i, j;