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Diffstat (limited to 'gnu/libg++/libg++/hash.cc')
| -rw-r--r-- | gnu/libg++/libg++/hash.cc | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/gnu/libg++/libg++/hash.cc b/gnu/libg++/libg++/hash.cc new file mode 100644 index 000000000000..4f16f9759890 --- /dev/null +++ b/gnu/libg++/libg++/hash.cc @@ -0,0 +1,56 @@ +/* +Copyright (C) 1990 Free Software Foundation + written by Doug Lea (dl@rocky.oswego.edu) + +This file is part of the GNU C++ Library. This library is free +software; you can redistribute it and/or modify it under the terms of +the GNU Library General Public License as published by the Free +Software Foundation; either version 2 of the License, or (at your +option) any later version. This library is distributed in the hope +that it will be useful, but WITHOUT ANY WARRANTY; without even the +implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR +PURPOSE. See the GNU Library General Public License for more details. +You should have received a copy of the GNU Library General Public +License along with this library; if not, write to the Free Software +Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. +*/ + +#ifdef __GNUG__ +#pragma implementation +#endif +#include <builtin.h> + +/* + some useful hash functions +*/ + +unsigned int hashpjw(const char* x) // From Dragon book, p436 +{ + unsigned int h = 0; + unsigned int g; + + while (*x != 0) + { + h = (h << 4) + *x++; + if ((g = h & 0xf0000000) != 0) + h = (h ^ (g >> 24)) ^ g; + } + return h; +} + +unsigned int multiplicativehash(int x) +{ + // uses a const close to golden ratio * pow(2,32) + return ((unsigned)x) * 2654435767; +} + + +unsigned int foldhash(double x) +{ + union { unsigned int i[2]; double d; } u; + u.d = x; + unsigned int u0 = u.i[0]; + unsigned int u1 = u.i[1]; + return u0 ^ u1; +} + |