RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2024-10-20 11:33:24 +02:00
Code Issues Projects Releases Wiki Activity

1. Make internal functions take const arguments where they should, just

Browse Source 
to be safe.
2. Make internal functions that return a carry/borrow return bool instead
   of uint64_t because the carry/borrow can only be in range [0,1].
3. Assert that the pointers to KnuthDiv are all different so that the
   result and operands can't overlap.
4. Add debug output to KnuthDiv function.
5. Fix a problem with KnuthDiv by separating the b's complement operation
   from the subtraction borrow operation. This fixes a wide range of
   division problems, but alas, not all of them.

llvm-svn: 34554
This commit is contained in:
Reid Spencer 2007-02-24 03:58:46 +00:00
parent e4ae26c339
commit b45646b14e
1 changed files with 61 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

82
lib/Support/APInt.cpp
View File

@ -12,8 +12,10 @@
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "apint"
#include "llvm/ADT/APInt.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include <cstring>
#include <cstdlib>
@ -189,8 +191,9 @@ APInt& APInt::operator--() {
/// add - This function adds the integer array x[] by integer array
/// y[] and returns the carry.
static uint64_t add(uint64_t dest[], uint64_t x[], uint64_t y[], uint32_t len) {
bool carry = 0;
static bool add(uint64_t *dest, const uint64_t *x, const uint64_t *y,
uint32_t len) {
bool carry = false;
for (uint32_t i = 0; i< len; ++i) {
uint64_t limit = std::min(x[i],y[i]); // must come first in case dest == x
dest[i] = x[i] + y[i] + carry;
@ -214,8 +217,8 @@ APInt& APInt::operator+=(const APInt& RHS) {
/// sub - This function subtracts the integer array x[] by
/// integer array y[], and returns the borrow-out carry.
static uint64_t sub(uint64_t *dest, const uint64_t *x, const uint64_t *y,
uint32_t len) {
static bool sub(uint64_t *dest, const uint64_t *x, const uint64_t *y,
uint32_t len) {
bool borrow = false;
for (uint32_t i = 0; i < len; ++i) {
uint64_t x_tmp = borrow ? x[i] - 1 : x[i];
@ -988,12 +991,19 @@ static void KnuthDiv(uint32_t *u, uint32_t *v, uint32_t *q, uint32_t* r,
assert(u && "Must provide dividend");
assert(v && "Must provide divisor");
assert(q && "Must provide quotient");
assert(u != v && u != q && v != q && "Must us different memory");
assert(n>1 && "n must be > 1");
// Knuth uses the value b as the base of the number system. In our case b
// is 2^31 so we just set it to -1u.
uint64_t b = uint64_t(1) << 32;
DEBUG(cerr << "KnuthDiv: m=" << m << " n=" << n << '\n');
DEBUG(cerr << "KnuthDiv: original:");
DEBUG(for (int i = m+n; i >=0; i--) cerr << " " << std::setbase(16) << u[i]);
DEBUG(cerr << " by");
DEBUG(for (int i = n; i >0; i--) cerr << " " << std::setbase(16) << v[i-1]);
DEBUG(cerr << '\n');
// D1. [Normalize.] Set d = b / (v[n-1] + 1) and multiply all the digits of
// u and v by d. Note that we have taken Knuth's advice here to use a power
// of 2 value for d such that d * v[n-1] >= b/2 (b is the base). A power of
@ -1018,10 +1028,16 @@ static void KnuthDiv(uint32_t *u, uint32_t *v, uint32_t *q, uint32_t* r,
}
}
u[m+n] = u_carry;
DEBUG(cerr << "KnuthDiv: normal:");
DEBUG(for (int i = m+n; i >=0; i--) cerr << " " << std::setbase(16) << u[i]);
DEBUG(cerr << " by");
DEBUG(for (int i = n; i >0; i--) cerr << " " << std::setbase(16) << v[i-1]);
DEBUG(cerr << '\n');
// D2. [Initialize j.] Set j to m. This is the loop counter over the places.
int j = m;
do {
DEBUG(cerr << "KnuthDiv: quotient digit #" << j << '\n');
// D3. [Calculate q'.].
// Set qp = (u[j+n]*b + u[j+n-1]) / v[n-1]. (qp=qprime=q')
// Set rp = (u[j+n]*b + u[j+n-1]) % v[n-1]. (rp=rprime=r')
@ -1031,41 +1047,54 @@ static void KnuthDiv(uint32_t *u, uint32_t *v, uint32_t *q, uint32_t* r,
// value qp is one too large, and it eliminates all cases where qp is two
// too large.
uint64_t dividend = ((uint64_t(u[j+n]) << 32) + u[j+n-1]);
DEBUG(cerr << "KnuthDiv: dividend == " << dividend << '\n');
uint64_t qp = dividend / v[n-1];
uint64_t rp = dividend % v[n-1];
if (qp == b || qp*v[n-2] > b*rp + u[j+n-2]) {
qp--;
rp += v[n-1];
if (rp < b) {
if (qp == b || qp*v[n-2] > b*rp + u[j+n-2]) {
qp--;
rp += v[n-1];
}
if (rp < b && (qp == b || qp*v[n-2] > b*rp + u[j+n-2])) {
qp--;
//rp += v[n-1];
}
}
DEBUG(cerr << "KnuthDiv: qp == " << qp << ", rp == " << rp << '\n');
// D4. [Multiply and subtract.] Replace (u[j+n]u[j+n-1]...u[j]) with
// (u[j+n]u[j+n-1]..u[j]) - qp * (v[n-1]...v[1]v[0]). This computation
// consists of a simple multiplication by a one-place number, combined with
// a subtraction. The digits (u[j+n]...u[j]) should be kept positive;
bool borrow = 0;
bool borrow = false;
for (uint32_t i = 0; i < n; ++i) {
uint64_t u_tmp = borrow ? u[j+i] - 1 : u[j+i];
uint64_t subtrahend = qp * v[i];
uint64_t u_tmp = borrow ? uint64_t(u[j+i] - 1) : uint64_t(u[j+i]);
uint64_t subtrahend = uint64_t(qp) * uint64_t(v[i]);
DEBUG(cerr << "KnuthDiv: u_tmp == " << u_tmp
<< ", subtrahend == " << subtrahend << '\n');
borrow = subtrahend > u_tmp || (borrow && u[j+i] == 0);
u[j+i] = u_tmp - subtrahend;
}
if (borrow) {
borrow = u[j+n] == 0; // Was result negative?
u[j+n]--; // handle the borrow
}
DEBUG(cerr << "KnuthDiv: after subtraction:");
DEBUG(for (int i = m+n; i >=0; i--) cerr << " " << u[i]);
DEBUG(cerr << '\n');
// if the result of this step is actually negative, (u[j+n]...u[j]) should
// be left as the true value plus b**(n+1), names as the b's complement of
// be left as the true value plus b**(n+1), namely as the b's complement of
// the true value, and a "borrow" to the left should be remembered.
//
if (borrow) {
borrow = u[j+n] == 0;
u[j+n]--;
// for (uint32_t i = 0; i < n; ++i) {
// u[j+i] = ~u[j+i] + 1; // b's complement
// }
bool carry = true;
for (uint32_t i = 0; i <= n; ++i) {
u[j+i] = ~u[j+i] + carry; // b's complement
carry = u[j+i] == 0;
}
}
DEBUG(cerr << "KnuthDiv: after complement:");
DEBUG(for (int i = m+n; i >=0; i--) cerr << " " << u[i]);
DEBUG(cerr << '\n');
// D5. [Test remainder.] Set q[j] = qp. If the result of step D4 was
// negative, go to step D6; otherwise go on to step D7.
@ -1080,16 +1109,23 @@ static void KnuthDiv(uint32_t *u, uint32_t *v, uint32_t *q, uint32_t* r,
// since it cancels with the borrow that occurred in D4.
bool carry = false;
for (uint32_t i = 0; i < n; i++) {
uint32_t save = u[j+i];
uint32_t limit = std::min(u[j+i],v[i]);
u[j+i] += v[i] + carry;
uint32_t limit = std::min(save,v[i]);
carry = u[j+i] < limit || (carry && u[j+1] == limit);
carry = u[j+i] < limit || (carry && u[j+i] == limit);
}
u[j+n] += carry;
}
DEBUG(cerr << "KnuthDiv: after correction:");
DEBUG(for (int i = m+n; i >=0; i--) cerr <<" " << u[i]);
DEBUG(cerr << "\nKnuthDiv: digit result = " << q[j] << '\n');
// D7. [Loop on j.] Decrease j by one. Now if j >= 0, go back to D3.
} while (--j >= 0);
DEBUG(cerr << "KnuthDiv: quotient:");
DEBUG(for (int i = m; i >=0; i--) cerr <<" " << q[i]);
DEBUG(cerr << '\n');
// D8. [Unnormalize]. Now q[...] is the desired quotient, and the desired
// remainder may be obtained by dividing u[...] by d. If r is non-null we
// compute the remainder (urem uses this).
@ -1098,11 +1134,15 @@ static void KnuthDiv(uint32_t *u, uint32_t *v, uint32_t *q, uint32_t* r,
// multiplication by d by using a shift left. So, all we have to do is
// shift right here. In order to mak
uint32_t carry = 0;
DEBUG(cerr << "KnuthDiv: remainder:");
for (int i = n-1; i >= 0; i--) {
r[i] = (u[i] >> shift) | carry;
carry = u[i] << shift;
DEBUG(cerr << " " << r[i]);
}
DEBUG(cerr << '\n');
}
DEBUG(cerr << std::setbase(10) << '\n');
}
// This function makes calling KnuthDiv a little more convenient. It uses