X-Git-Url: http://git.annexia.org/?a=blobdiff_plain;f=bitstring_c.c;h=5570f0506356edf1bfd30c9c3c53ae42a5fc0354;hb=ec13c41509db2b7fae9138cde2a8ea0b6d3b3699;hp=6faba8b214a4bd615bcc77af0c6333aa9ddd7b98;hpb=05e4823231b911aa103ebb0339a9d3519606a028;p=ocaml-bitstring.git

diff --git a/bitstring_c.c b/bitstring_c.c
index 6faba8b..5570f05 100644
--- a/bitstring_c.c
+++ b/bitstring_c.c
@@ -23,20 +23,94 @@
  * certain very frequently used functions.
  */
 
+#include <config.h>
+
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdint.h>
+#include <byteswap.h>
 
 #include <caml/mlvalues.h>
 #include <caml/fail.h>
 
-/* Return a mask of 0-31 bits wide. */
-CAMLprim value
-ocaml_bitstring_I_mask (value bitsv)
-{
-  int bits = Int_val (bitsv);
-
-  if (bits <= 31)
-    return Val_int ((1 << bits) - 1);
-  else
-    caml_invalid_argument ("Bitstring.I.mask");
-}
+/* Fastpath functions.  These are used in the common case for reading
+ * ints where the following conditions are known to be true:
+ * (a) the int size is a whole number of bytes (eg. 16, 24, 32, etc bits)
+ * (b) the access in the match is byte-aligned
+ * (c) the access in the underlying bitstring is byte-aligned
+ *
+ * These functions are all "noalloc" meaning they must not perform
+ * any OCaml allocations.  For this reason, when the function returns
+ * an int32 or int64, the OCaml code passes in the pre-allocated pointer
+ * to the return value.
+ *
+ * The final offset in the string is calculated by the OCaml (caller)
+ * code.  All we need to do is to read the string+offset and byteswap,
+ * sign-extend as necessary.
+ *
+ * There is one function for every combination of:
+ * (i) int size: 16, 32, 64 bits
+ * (ii) endian: bigendian, littleendian, nativeendian
+ * (iii) signed and unsigned
+ *
+ * XXX Future work: Expand this to 24, 40, 48, 56 bits.  This
+ * requires some extra work because sign-extension won't "just happen".
+ */
+
+#ifdef WORDS_BIGENDIAN
+#define swap_be(size,v)
+#define swap_le(size,v) v = bswap_##size (v)
+#define swap_ne(size,v)
+#else
+#define swap_be(size,v) v = bswap_##size (v)
+#define swap_le(size,v)
+#define swap_ne(size,v)
+#endif
+
+#define fastpath1(size,endian,signed,type)				\
+  CAMLprim value							\
+  ocaml_bitstring_extract_fastpath_int##size##_##endian##_##signed	\
+  (value strv, value offv)						\
+  {									\
+    type *ptr = (type *) ((void *) String_val (strv) + Int_val (offv));	\
+    type r;								\
+    r = *ptr;								\
+    swap_##endian(size,r);						\
+    return Val_int (r);							\
+  }
+
+fastpath1(16,be,unsigned,uint16_t)
+fastpath1(16,le,unsigned,uint16_t)
+fastpath1(16,ne,unsigned,uint16_t)
+fastpath1(16,be,signed,int16_t)
+fastpath1(16,le,signed,int16_t)
+fastpath1(16,ne,signed,int16_t)
+
+/* XXX This probably doesn't work on ARCH_ALIGN_INT64 platforms. */
+
+#define fastpath2(size,endian,signed,type,rval)				\
+  CAMLprim value							\
+  ocaml_bitstring_extract_fastpath_int##size##_##endian##_##signed	\
+  (value strv, value offv, value rv)					\
+  {									\
+    type *ptr = (type *) ((void *) String_val (strv) + Int_val (offv));	\
+    type r;								\
+    r = *ptr;								\
+    swap_##endian(size,r);						\
+    rval(rv) = r;							\
+    return rv;								\
+  }
+
+fastpath2(32,be,unsigned,uint32_t,Int32_val)
+fastpath2(32,le,unsigned,uint32_t,Int32_val)
+fastpath2(32,ne,unsigned,uint32_t,Int32_val)
+fastpath2(32,be,signed,int32_t,Int32_val)
+fastpath2(32,le,signed,int32_t,Int32_val)
+fastpath2(32,ne,signed,int32_t,Int32_val)
+
+fastpath2(64,be,unsigned,uint64_t,Int64_val)
+fastpath2(64,le,unsigned,uint64_t,Int64_val)
+fastpath2(64,ne,unsigned,uint64_t,Int64_val)
+fastpath2(64,be,signed,int64_t,Int64_val)
+fastpath2(64,le,signed,int64_t,Int64_val)
+fastpath2(64,ne,signed,int64_t,Int64_val)