irixKludges.C

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/*
 * See the dyninst/COPYRIGHT file for copyright information.
 * 
 * We provide the Paradyn Tools (below described as "Paradyn")
 * on an AS IS basis, and do not warrant its validity or performance.
 * We reserve the right to update, modify, or discontinue this
 * software at any time.  We shall have no obligation to supply such
 * updates or modifications or any other form of support to you.
 * 
 * By your use of Paradyn, you understand and agree that we (or any
 * other person or entity with proprietary rights in Paradyn) are
 * under no obligation to provide either maintenance services,
 * update services, notices of latent defects, or correction of
 * defects for Paradyn.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 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
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "common/h/headers.h"
#include "common/h/irixKludges.h"

// copied from solarisKludges.C
unsigned long long PDYN_div1000(unsigned long long in) {
   /* Divides by 1000 without an integer division instruction or library call, both of
    * which are slow.
    * We do only shifts, adds, and subtracts.
    *
    * We divide by 1000 in this way:
    * multiply by 1/1000, or multiply by (1/1000)*2^30 and then right-shift by 30.
    * So what is 1/1000 * 2^30?
    * It is 1,073,742.   (actually this is rounded)
    * So we can multiply by 1,073,742 and then right-shift by 30 (neat, eh?)
    *
    * Now for multiplying by 1,073,742...
    * 1,073,742 = (1,048,576 + 16384 + 8192 + 512 + 64 + 8 + 4 + 2)
    * or, slightly optimized:
    * = (1,048,576 + 16384 + 8192 + 512 + 64 + 16 - 2)
    * for a total of 8 shifts and 6 add/subs, or 14 operations.
    *
    */

   unsigned long long temp = in << 20; // multiply by 1,048,576
      // beware of overflow; left shift by 20 is quite a lot.
      // If you know that the input fits in 32 bits (4 billion) then
      // no problem.  But if it's much bigger then start worrying...

   temp += in << 14; // 16384
   temp += in << 13; // 8192
   temp += in << 9;  // 512
   temp += in << 6;  // 64
   temp += in << 4;  // 16
   temp -= in >> 2;  // 2

   return (temp >> 30); // divide by 2^30
}

// copied from solarisKludges.C
unsigned long long PDYN_divMillion(unsigned long long in) {
   /* Divides by 1,000,000 without an integer division instruction or library call,
    * both of which are slow.
    * We do only shifts, adds, and subtracts.
    *
    * We divide by 1,000,000 in this way:
    * multiply by 1/1,000,000, or multiply by (1/1,000,000)*2^30 and then right-shift
    * by 30.  So what is 1/1,000,000 * 2^30?
    * It is 1,074.   (actually this is rounded)
    * So we can multiply by 1,074 and then right-shift by 30 (neat, eh?)
    *
    * Now for multiplying by 1,074
    * 1,074 = (1024 + 32 + 16 + 2)
    * for a total of 4 shifts and 4 add/subs, or 8 operations.
    *
    * Note: compare with div1000 -- it's cheaper to divide by a million than
    *       by a thousand (!)
    *
    */

   unsigned long long temp = in << 10; // multiply by 1024
      // beware of overflow...if the input arg uses more than 52 bits
      // than start worrying about whether (in << 10) plus the smaller additions
      // we're gonna do next will fit in 64...

   temp += in << 5; // 32
   temp += in << 4; // 16
   temp += in << 1; // 2

   return (temp >> 30); // divide by 2^30
}

// copied from solarisKludges.C
unsigned long long PDYN_mulMillion(unsigned long long in) {
   unsigned long long result = in;

   /* multiply by 125 by multiplying by 128 and subtracting 3x */
   result = (result << 7) - result - result - result;

   /* multiply by 125 again, for a total of 15625x */
   result = (result << 7) - result - result - result;

   /* multiply by 64, for a total of 1,000,000x */
   result <<= 6;

   /* cost was: 3 shifts and 6 subtracts
    * cost of calling mul1000(mul1000()) would be: 6 shifts and 4 subtracts
    *
    * Another algorithm is to multiply by 2^6 and then 5^6.
    * The former is super-cheap (one shift); the latter is more expensive.
    * 5^6 = 15625 = 16384 - 512 - 256 + 8 + 1
    * so multiplying by 5^6 means 4 shift operations and 4 add/sub ops
    * so multiplying by 1000000 means 5 shift operations and 4 add/sub ops.
    * That may or may not be cheaper than what we're doing (3 shifts; 6 subtracts);
    * I'm not sure.  --ari
    */

   return result;
}