Compilation fails due to void pointer arithmetic (issue 24).

[ocaml-bitstring.git] / bitstring_c.c

diff --git a/bitstring_c.c b/bitstring_c.c
index 6faba8b..d376f76 100644 (file)
--- a/bitstring_c.c
+++ b/bitstring_c.c
@@ -23,20 +23,97 @@
  * certain very frequently used functions.
  */
 
+#include <config.h>
+
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdint.h>
+#include <byteswap.h>
+#include <string.h>
 
 #include <caml/mlvalues.h>
 #include <caml/fail.h>
+#include <caml/memory.h>
+#include <caml/alloc.h>
+
+/* 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 used to all be "noalloc" meaning they must not
+ * perform any OCaml allocations.  However starting with OCaml 4.02, a
+ * compiler optimization means that unforunately we now have to use
+ * ordinary alloc functions in some cases.
+ *
+ * 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 *) ((char *) String_val (strv) + Int_val (offv));        \
+    type r;                                                            \
+    memcpy(&r, ptr, sizeof(r));                                        \
+    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)
+
+#define fastpath2(size,endian,signed,type,copy)                                \
+  CAMLprim value                                                       \
+  ocaml_bitstring_extract_fastpath_int##size##_##endian##_##signed     \
+  (value strv, value offv)                                              \
+  {                                                                    \
+    CAMLparam2 (strv, offv);                                            \
+    CAMLlocal1 (rv);                                                    \
+    type *ptr = (type *) ((char *) String_val (strv) + Int_val (offv));        \
+    type r;                                                            \
+    memcpy(&r, ptr, sizeof(r));                                         \
+    swap_##endian(size,r);                                             \
+    rv = copy (r);                                                      \
+    CAMLreturn (rv);                                                    \
+  }
+
+fastpath2(32,be,unsigned,uint32_t,caml_copy_int32)
+fastpath2(32,le,unsigned,uint32_t,caml_copy_int32)
+fastpath2(32,ne,unsigned,uint32_t,caml_copy_int32)
+fastpath2(32,be,signed,int32_t,caml_copy_int32)
+fastpath2(32,le,signed,int32_t,caml_copy_int32)
+fastpath2(32,ne,signed,int32_t,caml_copy_int32)
 
-/* 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");
-}
+fastpath2(64,be,unsigned,uint64_t,caml_copy_int64)
+fastpath2(64,le,unsigned,uint64_t,caml_copy_int64)
+fastpath2(64,ne,unsigned,uint64_t,caml_copy_int64)
+fastpath2(64,be,signed,int64_t,caml_copy_int64)
+fastpath2(64,le,signed,int64_t,caml_copy_int64)
+fastpath2(64,ne,signed,int64_t,caml_copy_int64)