bitstring_c.c

   1 /* Bitstring library.
   2  * Copyright (C) 2008 Red Hat Inc., Richard W.M. Jones
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2 of the License, or (at your option) any later version,
   8  * with the OCaml linking exception described in COPYING.LIB.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public
  16  * License along with this library; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  18  *
  19  * $Id: bitstring.ml 146 2008-08-20 16:58:33Z richard.wm.jones $
  20  */
  21
  22 /* This file contains hand-coded, optimized C implementations of
  23  * certain very frequently used functions.
  24  */
  25
  26 #include <config.h>
  27
  28 #include <stdio.h>
  29 #include <stdlib.h>
  30 #include <stdint.h>
  31 #include <byteswap.h>
  32 #include <string.h>
  33
  34 #include <caml/mlvalues.h>
  35 #include <caml/fail.h>
  36 #include <caml/memory.h>
  37 #include <caml/alloc.h>
  38
  39 /* Fastpath functions.  These are used in the common case for reading
  40  * ints where the following conditions are known to be true:
  41  * (a) the int size is a whole number of bytes (eg. 16, 24, 32, etc bits)
  42  * (b) the access in the match is byte-aligned
  43  * (c) the access in the underlying bitstring is byte-aligned
  44  *
  45  * These functions used to all be "noalloc" meaning they must not
  46  * perform any OCaml allocations.  However starting with OCaml 4.02, a
  47  * compiler optimization means that unforunately we now have to use
  48  * ordinary alloc functions in some cases.
  49  *
  50  * The final offset in the string is calculated by the OCaml (caller)
  51  * code.  All we need to do is to read the string+offset and byteswap,
  52  * sign-extend as necessary.
  53  *
  54  * There is one function for every combination of:
  55  * (i) int size: 16, 32, 64 bits
  56  * (ii) endian: bigendian, littleendian, nativeendian
  57  * (iii) signed and unsigned
  58  *
  59  * XXX Future work: Expand this to 24, 40, 48, 56 bits.  This
  60  * requires some extra work because sign-extension won't "just happen".
  61  */
  62
  63 #ifdef WORDS_BIGENDIAN
  64 #define swap_be(size,v)
  65 #define swap_le(size,v) v = bswap_##size (v)
  66 #define swap_ne(size,v)
  67 #else
  68 #define swap_be(size,v) v = bswap_##size (v)
  69 #define swap_le(size,v)
  70 #define swap_ne(size,v)
  71 #endif
  72
  73 #define fastpath1(size,endian,signed,type)                              \
  74   CAMLprim value                                                        \
  75   ocaml_bitstring_extract_fastpath_int##size##_##endian##_##signed      \
  76   (value strv, value offv)                                              \
  77   {                                                                     \
  78     type *ptr = (type *) ((char *) String_val (strv) + Int_val (offv)); \
  79     type r;                                                             \
  80     memcpy(&r, ptr, sizeof(r));                                 \
  81     swap_##endian(size,r);                                              \
  82     return Val_int (r);                                                 \
  83   }
  84
  85 fastpath1(16,be,unsigned,uint16_t)
  86 fastpath1(16,le,unsigned,uint16_t)
  87 fastpath1(16,ne,unsigned,uint16_t)
  88 fastpath1(16,be,signed,int16_t)
  89 fastpath1(16,le,signed,int16_t)
  90 fastpath1(16,ne,signed,int16_t)
  91
  92 #define fastpath2(size,endian,signed,type,copy)                         \
  93   CAMLprim value                                                        \
  94   ocaml_bitstring_extract_fastpath_int##size##_##endian##_##signed      \
  95   (value strv, value offv)                                              \
  96   {                                                                     \
  97     CAMLparam2 (strv, offv);                                            \
  98     CAMLlocal1 (rv);                                                    \
  99     type *ptr = (type *) ((char *) String_val (strv) + Int_val (offv)); \
 100     type r;                                                             \
 101     memcpy(&r, ptr, sizeof(r));                                         \
 102     swap_##endian(size,r);                                              \
 103     rv = copy (r);                                                      \
 104     CAMLreturn (rv);                                                    \
 105   }
 106
 107 fastpath2(32,be,unsigned,uint32_t,caml_copy_int32)
 108 fastpath2(32,le,unsigned,uint32_t,caml_copy_int32)
 109 fastpath2(32,ne,unsigned,uint32_t,caml_copy_int32)
 110 fastpath2(32,be,signed,int32_t,caml_copy_int32)
 111 fastpath2(32,le,signed,int32_t,caml_copy_int32)
 112 fastpath2(32,ne,signed,int32_t,caml_copy_int32)
 113
 114 fastpath2(64,be,unsigned,uint64_t,caml_copy_int64)
 115 fastpath2(64,le,unsigned,uint64_t,caml_copy_int64)
 116 fastpath2(64,ne,unsigned,uint64_t,caml_copy_int64)
 117 fastpath2(64,be,signed,int64_t,caml_copy_int64)
 118 fastpath2(64,le,signed,int64_t,caml_copy_int64)
 119 fastpath2(64,ne,signed,int64_t,caml_copy_int64)