From be98f29f51350c24136c191f01af3fbfe340ef78 Mon Sep 17 00:00:00 2001
From: Chris Dyer <cdyer@cs.cmu.edu>
Date: Mon, 13 Dec 2010 16:18:34 -0500
Subject: new version of kenlm

---
 klm/util/bit_packing.hh | 48 ++++++++++++++++++++++++++++++------------------
 1 file changed, 30 insertions(+), 18 deletions(-)

(limited to 'klm/util/bit_packing.hh')

diff --git a/klm/util/bit_packing.hh b/klm/util/bit_packing.hh
index 422ed873..0fd39d7f 100644
--- a/klm/util/bit_packing.hh
+++ b/klm/util/bit_packing.hh
@@ -6,56 +6,68 @@
 #include <assert.h>
 #ifdef __APPLE__
 #include <architecture/byte_order.h>
-#else
+#elif __linux__
 #include <endian.h>
-#endif
+#else
+#include <arpa/nameser_compat.h>
+#endif 
 
 #include <inttypes.h>
 
-#if __BYTE_ORDER != __LITTLE_ENDIAN
-#error The bit aligned storage functions assume little endian architecture
-#endif
-
 namespace util {
 
 /* WARNING WARNING WARNING:
  * The write functions assume that memory is zero initially.  This makes them
  * faster and is the appropriate case for mmapped language model construction.
  * These routines assume that unaligned access to uint64_t is fast and that
- * storage is little endian.  This is the case on x86_64.  It may not be the
- * case on 32-bit x86 but my target audience is large language models for which
- * 64-bit is necessary.  
+ * storage is little endian.  This is the case on x86_64.  I'm not sure how 
+ * fast unaligned 64-bit access is on x86 but my target audience is large
+ * language models for which 64-bit is necessary.  
+ *
+ * Call the BitPackingSanity function to sanity check.  Calling once suffices,
+ * but it may be called multiple times when that's inconvenient.  
  */
 
+inline uint8_t BitPackShift(uint8_t bit, uint8_t length) {
+// Fun fact: __BYTE_ORDER is wrong on Solaris Sparc, but the version without __ is correct.  
+#if BYTE_ORDER == LITTLE_ENDIAN
+  return bit;
+#elif BYTE_ORDER == BIG_ENDIAN
+  return 64 - length - bit;
+#else
+#error "Bit packing code isn't written for your byte order."
+#endif
+}
+
 /* Pack integers up to 57 bits using their least significant digits. 
  * The length is specified using mask:
  * Assumes mask == (1 << length) - 1 where length <= 57.   
  */
-inline uint64_t ReadInt57(const void *base, uint8_t bit, uint64_t mask) {
-  return (*reinterpret_cast<const uint64_t*>(base) >> bit) & mask;
+inline uint64_t ReadInt57(const void *base, uint8_t bit, uint8_t length, uint64_t mask) {
+  return (*reinterpret_cast<const uint64_t*>(base) >> BitPackShift(bit, length)) & mask;
 }
-/* Assumes value <= mask and mask == (1 << length) - 1 where length <= 57.
+/* Assumes value < (1 << length) and length <= 57.
  * Assumes the memory is zero initially. 
  */
-inline void WriteInt57(void *base, uint8_t bit, uint64_t value) {
-  *reinterpret_cast<uint64_t*>(base) |= (value << bit);
+inline void WriteInt57(void *base, uint8_t bit, uint8_t length, uint64_t value) {
+  *reinterpret_cast<uint64_t*>(base) |= (value << BitPackShift(bit, length));
 }
 
 namespace detail { typedef union { float f; uint32_t i; } FloatEnc; }
 inline float ReadFloat32(const void *base, uint8_t bit) {
   detail::FloatEnc encoded;
-  encoded.i = *reinterpret_cast<const uint64_t*>(base) >> bit;
+  encoded.i = *reinterpret_cast<const uint64_t*>(base) >> BitPackShift(bit, 32);
   return encoded.f;
 }
 inline void WriteFloat32(void *base, uint8_t bit, float value) {
   detail::FloatEnc encoded;
   encoded.f = value;
-  WriteInt57(base, bit, encoded.i);
+  WriteInt57(base, bit, 32, encoded.i);
 }
 
 inline float ReadNonPositiveFloat31(const void *base, uint8_t bit) {
   detail::FloatEnc encoded;
-  encoded.i = *reinterpret_cast<const uint64_t*>(base) >> bit;
+  encoded.i = *reinterpret_cast<const uint64_t*>(base) >> BitPackShift(bit, 31);
   // Sign bit set means negative.  
   encoded.i |= 0x80000000;
   return encoded.f;
@@ -65,7 +77,7 @@ inline void WriteNonPositiveFloat31(void *base, uint8_t bit, float value) {
   detail::FloatEnc encoded;
   encoded.f = value;
   encoded.i &= ~0x80000000;
-  WriteInt57(base, bit, encoded.i);
+  WriteInt57(base, bit, 31, encoded.i);
 }
 
 void BitPackingSanity();
-- 
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