Create Subversion repository

git-svn-id: http://svn.code.sf.net/p/netpbm/code/trunk@1 9d0c8265-081b-0410-96cb-a4ca84ce46f8

1 files changed, 65 insertions, 0 deletions

diff --git a/lib/util/wordaccess.h b/lib/util/wordaccess.h
new file mode 100644
index 00000000..28963aee
--- /dev/null
+++ b/lib/util/wordaccess.h
@@ -0,0 +1,65 @@
+#ifndef WORDACCESS_H_INCLUDED
+#define WORDACCESS_H_INCLUDED
+
+/* These are facilities for accessing data in C programs in ways that
+   exploit the way the machine defines words in order to squeeze out
+   speed and CPU efficiency.
+
+   In particular, routines in this file exploit the endianness of the
+   machine and use explicit machine instructions to access C
+   variables.
+
+   A word is the amount of data that fits in a register; the amount of
+   data that a single machine instruction can process.  For example,
+   on IA32, a word is 32 bits because a single load or store
+   instruction moves that many bits and a single add instruction
+   operates on that many bits.
+
+
+   These facilities revolve around two data types:  wordInt and
+   wordIntBytes.
+
+   wordint is an unsigned integer with precision (size) of one word.
+   It is just the number -- nothing is implied about how it is
+   represented in memory.
+
+   wordintBytes is an array of bytes that represent a word-sized
+   unsigned integer.  x[0] is the high order 8 digits of the binary
+   coding of the integer, x[1] the next highest 8 digits, etc.
+   Note that it has big-endian form, regardless of what endianness the
+   underlying machine uses.
+
+   The actual size of word differs by machine.  Usually it is 32 or 64
+   bits.  Logically it can be as small as one byte.  Fixed bit sequences
+   in each program impose a lower limit of word width.  For example, the
+   longest bit sequence in pbmtog3 has 13 bits, so an 8-bit word won't
+   work with that.
+
+   We also assume that a char is 8 bits.
+*/
+#if (!defined(WORDACCESS_GENERIC) \
+     && defined(__GNUC__) && defined(__GLIBC__) \
+     && (__GNUC__ * 100 + __GNUC_MINOR__ >= 304) )
+
+    #if BYTE_ORDER==BIG_ENDIAN    /* defined by GCC */
+
+        #include "wordaccess_gcc3_be.h"
+
+    #elif defined(__ia64__) || defined(__amd64__) || defined(__x86_64__)
+         /* all these macros are defined by GCC */
+
+        #include "wordaccess_64_le.h"
+
+    #else
+
+        #include "wordaccess_gcc3_le.h"
+
+    #endif
+
+#else
+
+    #include "wordaccess_generic.h"
+
+#endif
+
+#endif