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
  33 #include <caml/mlvalues.h>
  34 #include <caml/fail.h>
  35
  36 /* Fastpath functions.  These are used in the common case for reading
  37  * ints where the following conditions are known to be true:
  38  * (a) the int size is a whole number of bytes (eg. 16, 24, 32, etc bits)
  39  * (b) the access in the match is byte-aligned
  40  * (c) the access in the underlying bitstring is byte-aligned
  41  *
  42  * These functions are all "noalloc" meaning they must not perform
  43  * any OCaml allocations.  For this reason, when the function returns
  44  * an int32 or int64, the OCaml code passes in the pre-allocated pointer
  45  * to the return value.
  46  *
  47  * The final offset in the string is calculated by the OCaml (caller)
  48  * code.  All we need to do is to read the string+offset and byteswap,
  49  * sign-extend as necessary.
  50  *
  51  * There is one function for every combination of:
  52  * (i) int size: 16, 32, 64 bits
  53  * (ii) endian: bigendian, littleendian, nativeendian
  54  * (iii) signed and unsigned
  55  *
  56  * XXX Future work: Expand this to 24, 40, 48, 56 bits.  This
  57  * requires some extra work because sign-extension won't "just happen".
  58  */
  59
  60 #ifdef WORDS_BIGENDIAN
  61 #define swap_be(size,v)
  62 #define swap_le(size,v) v = bswap_##size (v)
  63 #define swap_ne(size,v)
  64 #else
  65 #define swap_be(size,v) v = bswap_##size (v)
  66 #define swap_le(size,v)
  67 #define swap_ne(size,v)
  68 #endif
  69
  70 #define fastpath1(size,endian,signed,type)                              \
  71   CAMLprim value                                                        \
  72   ocaml_bitstring_extract_fastpath_int##size##_##endian##_##signed      \
  73   (value strv, value offv)                                              \
  74   {                                                                     \
  75     type *ptr = (type *) ((void *) String_val (strv) + Int_val (offv)); \
  76     type r;                                                             \
  77     r = *ptr;                                                           \
  78     swap_##endian(size,r);                                              \
  79     return Val_int (r);                                                 \
  80   }
  81
  82 fastpath1(16,be,unsigned,uint16_t)
  83 fastpath1(16,le,unsigned,uint16_t)
  84 fastpath1(16,ne,unsigned,uint16_t)
  85 fastpath1(16,be,signed,int16_t)
  86 fastpath1(16,le,signed,int16_t)
  87 fastpath1(16,ne,signed,int16_t)
  88
  89 /* XXX This probably doesn't work on ARCH_ALIGN_INT64 platforms. */
  90
  91 #define fastpath2(size,endian,signed,type,rval)                         \
  92   CAMLprim value                                                        \
  93   ocaml_bitstring_extract_fastpath_int##size##_##endian##_##signed      \
  94   (value strv, value offv, value rv)                                    \
  95   {                                                                     \
  96     type *ptr = (type *) ((void *) String_val (strv) + Int_val (offv)); \
  97     type r;                                                             \
  98     r = *ptr;                                                           \
  99     swap_##endian(size,r);                                              \
 100     rval(rv) = r;                                                       \
 101     return rv;                                                          \
 102   }
 103
 104 fastpath2(32,be,unsigned,uint32_t,Int32_val)
 105 fastpath2(32,le,unsigned,uint32_t,Int32_val)
 106 fastpath2(32,ne,unsigned,uint32_t,Int32_val)
 107 fastpath2(32,be,signed,int32_t,Int32_val)
 108 fastpath2(32,le,signed,int32_t,Int32_val)
 109 fastpath2(32,ne,signed,int32_t,Int32_val)
 110
 111 fastpath2(64,be,unsigned,uint64_t,Int64_val)
 112 fastpath2(64,le,unsigned,uint64_t,Int64_val)
 113 fastpath2(64,ne,unsigned,uint64_t,Int64_val)
 114 fastpath2(64,be,signed,int64_t,Int64_val)
 115 fastpath2(64,le,signed,int64_t,Int64_val)
 116 fastpath2(64,ne,signed,int64_t,Int64_val)