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Issue 532003004: Generalized division via multiplication. (Closed) Base URL: https://v8.googlecode.com/svn/branches/bleeding_edge
Patch Set: Rebased Created 6 years, 3 months ago
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1 // Copyright (c) 1994-2006 Sun Microsystems Inc. 1 // Copyright (c) 1994-2006 Sun Microsystems Inc.
2 // All Rights Reserved. 2 // All Rights Reserved.
3 // 3 //
4 // Redistribution and use in source and binary forms, with or without 4 // Redistribution and use in source and binary forms, with or without
5 // modification, are permitted provided that the following conditions are 5 // modification, are permitted provided that the following conditions are
6 // met: 6 // met:
7 // 7 //
8 // - Redistributions of source code must retain the above copyright notice, 8 // - Redistributions of source code must retain the above copyright notice,
9 // this list of conditions and the following disclaimer. 9 // this list of conditions and the following disclaimer.
10 // 10 //
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1564 EnsureSpace ensure_space(assembler_); 1564 EnsureSpace ensure_space(assembler_);
1565 assembler_->RecordRelocInfo(RelocInfo::POSITION, state_.current_position); 1565 assembler_->RecordRelocInfo(RelocInfo::POSITION, state_.current_position);
1566 state_.written_position = state_.current_position; 1566 state_.written_position = state_.current_position;
1567 written = true; 1567 written = true;
1568 } 1568 }
1569 1569
1570 // Return whether something was written. 1570 // Return whether something was written.
1571 return written; 1571 return written;
1572 } 1572 }
1573 1573
1574
1575 MultiplierAndShift::MultiplierAndShift(int32_t d) {
1576 DCHECK(d <= -2 || 2 <= d);
1577 const uint32_t two31 = 0x80000000;
1578 uint32_t ad = Abs(d);
1579 uint32_t t = two31 + (uint32_t(d) >> 31);
1580 uint32_t anc = t - 1 - t % ad; // Absolute value of nc.
1581 int32_t p = 31; // Init. p.
1582 uint32_t q1 = two31 / anc; // Init. q1 = 2**p/|nc|.
1583 uint32_t r1 = two31 - q1 * anc; // Init. r1 = rem(2**p, |nc|).
1584 uint32_t q2 = two31 / ad; // Init. q2 = 2**p/|d|.
1585 uint32_t r2 = two31 - q2 * ad; // Init. r2 = rem(2**p, |d|).
1586 uint32_t delta;
1587 do {
1588 p++;
1589 q1 *= 2; // Update q1 = 2**p/|nc|.
1590 r1 *= 2; // Update r1 = rem(2**p, |nc|).
1591 if (r1 >= anc) { // Must be an unsigned comparison here.
1592 q1++;
1593 r1 = r1 - anc;
1594 }
1595 q2 *= 2; // Update q2 = 2**p/|d|.
1596 r2 *= 2; // Update r2 = rem(2**p, |d|).
1597 if (r2 >= ad) { // Must be an unsigned comparison here.
1598 q2++;
1599 r2 = r2 - ad;
1600 }
1601 delta = ad - r2;
1602 } while (q1 < delta || (q1 == delta && r1 == 0));
1603 int32_t mul = static_cast<int32_t>(q2 + 1);
1604 multiplier_ = (d < 0) ? -mul : mul;
1605 shift_ = p - 32;
1606 }
1607
1608 } } // namespace v8::internal 1574 } } // namespace v8::internal
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