gcc/hash-table.c

   1 /* A type-safe hash table template.
   2    Copyright (C) 2012-2015 Free Software Foundation, Inc.
   3    Contributed by Lawrence Crowl <crowl@google.com>
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify it under
   8 the terms of the GNU General Public License as published by the Free
   9 Software Foundation; either version 3, or (at your option) any later
  10 version.
  11
  12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15 for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21
  22 /* This file implements a typed hash table.
  23    The implementation borrows from libiberty's hashtab.  */
  24
  25 #ifdef GENERATOR_FILE
  26 #include "bconfig.h"
  27 #else
  28 #include "config.h"
  29 #endif
  30 #include "system.h"
  31 #include "coretypes.h"
  32 #include "hash-table.h"
  33
  34
  35 /* Table of primes and multiplicative inverses.
  36
  37    Note that these are not minimally reduced inverses.  Unlike when generating
  38    code to divide by a constant, we want to be able to use the same algorithm
  39    all the time.  All of these inverses (are implied to) have bit 32 set.
  40
  41    For the record, here's the function that computed the table; it's a
  42    vastly simplified version of the function of the same name from gcc.  */
  43
  44 struct prime_ent const prime_tab[] = {
  45   {          7, 0x24924925, 0x9999999b, 2 },
  46   {         13, 0x3b13b13c, 0x745d1747, 3 },
  47   {         31, 0x08421085, 0x1a7b9612, 4 },
  48   {         61, 0x0c9714fc, 0x15b1e5f8, 5 },
  49   {        127, 0x02040811, 0x0624dd30, 6 },
  50   {        251, 0x05197f7e, 0x073260a5, 7 },
  51   {        509, 0x01824366, 0x02864fc8, 8 },
  52   {       1021, 0x00c0906d, 0x014191f7, 9 },
  53   {       2039, 0x0121456f, 0x0161e69e, 10 },
  54   {       4093, 0x00300902, 0x00501908, 11 },
  55   {       8191, 0x00080041, 0x00180241, 12 },
  56   {      16381, 0x000c0091, 0x00140191, 13 },
  57   {      32749, 0x002605a5, 0x002a06e6, 14 },
  58   {      65521, 0x000f00e2, 0x00110122, 15 },
  59   {     131071, 0x00008001, 0x00018003, 16 },
  60   {     262139, 0x00014002, 0x0001c004, 17 },
  61   {     524287, 0x00002001, 0x00006001, 18 },
  62   {    1048573, 0x00003001, 0x00005001, 19 },
  63   {    2097143, 0x00004801, 0x00005801, 20 },
  64   {    4194301, 0x00000c01, 0x00001401, 21 },
  65   {    8388593, 0x00001e01, 0x00002201, 22 },
  66   {   16777213, 0x00000301, 0x00000501, 23 },
  67   {   33554393, 0x00001381, 0x00001481, 24 },
  68   {   67108859, 0x00000141, 0x000001c1, 25 },
  69   {  134217689, 0x000004e1, 0x00000521, 26 },
  70   {  268435399, 0x00000391, 0x000003b1, 27 },
  71   {  536870909, 0x00000019, 0x00000029, 28 },
  72   { 1073741789, 0x0000008d, 0x00000095, 29 },
  73   { 2147483647, 0x00000003, 0x00000007, 30 },
  74   /* Avoid "decimal constant so large it is unsigned" for 4294967291.  */
  75   { 0xfffffffb, 0x00000006, 0x00000008, 31 }
  76 };
  77
  78 /* The following function returns an index into the above table of the
  79    nearest prime number which is greater than N, and near a power of two. */
  80
  81 unsigned int
  82 hash_table_higher_prime_index (unsigned long n)
  83 {
  84   unsigned int low = 0;
  85   unsigned int high = sizeof (prime_tab) / sizeof (prime_tab[0]);
  86
  87   while (low != high)
  88     {
  89       unsigned int mid = low + (high - low) / 2;
  90       if (n > prime_tab[mid].prime)
  91         low = mid + 1;
  92       else
  93         high = mid;
  94     }
  95
  96   /* If we've run out of primes, abort.  */
  97   gcc_assert (n <= prime_tab[low].prime);
  98
  99   return low;
 100 }
 101