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
  37 /* Fastpath functions.  These are used in the common case for reading
  38  * ints where the following conditions are known to be true:
  39  * (a) the int size is a whole number of bytes (eg. 16, 24, 32, etc bits)
  40  * (b) the access in the match is byte-aligned
  41  * (c) the access in the underlying bitstring is byte-aligned
  42  *
  43  * These functions are all "noalloc" meaning they must not perform
  44  * any OCaml allocations.  For this reason, when the function returns
  45  * an int32 or int64, the OCaml code passes in the pre-allocated pointer
  46  * to the return value.
  47  *
  48  * The final offset in the string is calculated by the OCaml (caller)
  49  * code.  All we need to do is to read the string+offset and byteswap,
  50  * sign-extend as necessary.
  51  *
  52  * There is one function for every combination of:
  53  * (i) int size: 16, 32, 64 bits
  54  * (ii) endian: bigendian, littleendian, nativeendian
  55  * (iii) signed and unsigned
  56  *
  57  * XXX Future work: Expand this to 24, 40, 48, 56 bits.  This
  58  * requires some extra work because sign-extension won't "just happen".
  59  */
  60
  61 #ifdef WORDS_BIGENDIAN
  62 #define swap_be(size,v)
  63 #define swap_le(size,v) v = bswap_##size (v)
  64 #define swap_ne(size,v)
  65 #else
  66 #define swap_be(size,v) v = bswap_##size (v)
  67 #define swap_le(size,v)
  68 #define swap_ne(size,v)
  69 #endif
  70
  71 #define fastpath1(size,endian,signed,type)                              \
  72   CAMLprim value                                                        \
  73   ocaml_bitstring_extract_fastpath_int##size##_##endian##_##signed      \
  74   (value strv, value offv)                                              \
  75   {                                                                     \
  76     type *ptr = (type *) ((void *) String_val (strv) + Int_val (offv)); \
  77     type r;                                                             \
  78     memcpy(&r, ptr, sizeof(r));                                 \
  79     swap_##endian(size,r);                                              \
  80     return Val_int (r);                                                 \
  81   }
  82
  83 fastpath1(16,be,unsigned,uint16_t)
  84 fastpath1(16,le,unsigned,uint16_t)
  85 fastpath1(16,ne,unsigned,uint16_t)
  86 fastpath1(16,be,signed,int16_t)
  87 fastpath1(16,le,signed,int16_t)
  88 fastpath1(16,ne,signed,int16_t)
  89
  90 #define fastpath2(size,endian,signed,type,rval)                         \
  91   CAMLprim value                                                        \
  92   ocaml_bitstring_extract_fastpath_int##size##_##endian##_##signed      \
  93   (value strv, value offv, value rv)                                    \
  94   {                                                                     \
  95     type *ptr = (type *) ((void *) String_val (strv) + Int_val (offv)); \
  96     type r;                                                             \
  97     memcpy(&r, ptr, sizeof(r));                                 \
  98     swap_##endian(size,r);                                              \
  99     rval(rv) = r;                                                       \
 100     return rv;                                                          \
 101   }
 102
 103 fastpath2(32,be,unsigned,uint32_t,Int32_val)
 104 fastpath2(32,le,unsigned,uint32_t,Int32_val)
 105 fastpath2(32,ne,unsigned,uint32_t,Int32_val)
 106 fastpath2(32,be,signed,int32_t,Int32_val)
 107 fastpath2(32,le,signed,int32_t,Int32_val)
 108 fastpath2(32,ne,signed,int32_t,Int32_val)
 109
 110 /* Special care needs to be taken on ARCH_ALIGN_INT64 platforms
 111    (hppa and sparc in Debian). */
 112
 113 #ifdef ARCH_ALIGN_INT64
 114 #include <caml/memory.h>
 115 #include <caml/alloc.h>
 116 #define fastpath3(size,endian,signed,type,rval)                         \
 117   CAMLprim value                                                        \
 118   ocaml_bitstring_extract_fastpath_int##size##_##endian##_##signed      \
 119   (value strv, value offv, value rv)                                    \
 120   {                                                                     \
 121     type *ptr = (type *) ((void *) String_val (strv) + Int_val (offv)); \
 122     type r;                                                             \
 123     memcpy(&r, ptr, sizeof(r));                                 \
 124     swap_##endian(size,r);                                              \
 125     memcpy(Data_custom_val(rv), &r, sizeof(r));                 \
 126     return rv;                                                          \
 127   }
 128
 129 #else
 130 #define fastpath3 fastpath2
 131 #endif
 132
 133 fastpath3(64,be,unsigned,uint64_t,Int64_val)
 134 fastpath3(64,le,unsigned,uint64_t,Int64_val)
 135 fastpath3(64,ne,unsigned,uint64_t,Int64_val)
 136 fastpath3(64,be,signed,int64_t,Int64_val)
 137 fastpath3(64,le,signed,int64_t,Int64_val)
 138 fastpath3(64,ne,signed,int64_t,Int64_val)