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From: "bonzini at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: java-prs@gcc.gnu.org Subject: [Bug java/23283] Sun's JIT faster than gcc for Random.nextDouble Date: Tue, 23 Aug 2005 14:48:00 -0000 [thread overview] Message-ID: <20050823144852.615.qmail@sourceware.org> (raw) In-Reply-To: <20050808100453.23283.netzberg@gmail.com> ------- Additional Comments From bonzini at gcc dot gnu dot org 2005-08-23 14:48 ------- Yes, I think that most invocations of next should be inlined, and wrapped in a single synchronized block. Apart from that, I am pretty sure that here seed = (seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1); return (int) (seed >>> (48 - bits)); it makes no difference if you do the AND or not. So nextDouble could be implemented as: long first; long second; synchronized (this) { seed = (seed * 0x5DEECE66DL + 0xBL); first = (seed & 0x0000FFFFFFC00000L) << 5; seed = (seed * 0x5DEECE66DL + 0xBL); second = (seed >> 21) & 0x7FFFFFF; } return (first | second) / (double) (1L << 53); Similarly, for nextFloat float f; int bits; synchronized (this) { seed = (seed * 0x5DEECE66DL + 0xBL); bits = (int) (seed >> 24); } return bits / 16777216.0f; nextInt int bits; synchronized (this) { seed = (seed * 0x5DEECE66DL + 0xBL); bits = (int) (seed >> 16); } nextLong long first, second; synchronized (this) { seed = (seed * 0x5DEECE66DL + 0xBL); first = (seed << 16) & 0xFFFFFFFF00000000L; seed = (seed * 0x5DEECE66DL + 0xBL); second = (seed >> 16) & 0xFFFFFFFFL; } return first | second; nextInt (n) int bits; synchronized (seed) { seed = (seed * 0x5DEECE66DL + 0xBL); bits = (int) (seed >> 17); } if ((n & -n) == n) // i.e., n is a power of 2 return (int)((n * (long) bits) >> 31); int bits, val; val = bits % n; if (bits - val + n - 1 < 0) synchronized (seed) { do { seed = (seed * 0x5DEECE66DL + 0xBL); bits = (int) (seed >> 17); } while (bits - val + n - 1 < 0); } return val; nextBoolean boolean bit; synchronized (this) { seed = (seed * 0x5DEECE66DL + 0xBL); bit = (seed & 0x800000000000) != 0; } return bit; And I left out nextBytes, I know. Also these are untested, which is why I'm not preparing a full patch. Paolo -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23283
next prev parent reply other threads:[~2005-08-23 14:48 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2005-08-08 10:04 [Bug java/23283] New: Java interpreter significantly faster than gcc?! netzberg at gmail dot com 2005-08-08 13:32 ` [Bug java/23283] Sun's JIT faster than gcc pinskia at gcc dot gnu dot org 2005-08-08 13:33 ` [Bug java/23283] Sun's JIT faster than gcc for Random.nextDouble pinskia at gcc dot gnu dot org 2005-08-23 14:15 ` tromey at gcc dot gnu dot org 2005-08-23 14:31 ` mark at klomp dot org 2005-08-23 14:48 ` bonzini at gcc dot gnu dot org [this message] 2005-08-23 14:51 ` bonzini at gcc dot gnu dot org
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