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glibc/sysdeps/ieee754/dbl-64/mpa.c

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/*
* IBM Accurate Mathematical Library
* written by International Business Machines Corp.
* Copyright (C) 2001-2017 Free Software Foundation, Inc.
*
* This program 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 program 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 program; if not, see <http://www.gnu.org/licenses/>.
*/
/************************************************************************/
/* MODULE_NAME: mpa.c */
/* */
/* FUNCTIONS: */
/* mcr */
/* acr */
/* cpy */
/* norm */
/* denorm */
/* mp_dbl */
/* dbl_mp */
/* add_magnitudes */
/* sub_magnitudes */
/* add */
/* sub */
/* mul */
/* inv */
/* dvd */
/* */
/* Arithmetic functions for multiple precision numbers. */
/* Relative errors are bounded */
/************************************************************************/
#include "endian.h"
#include "mpa.h"
#include <sys/param.h>
#include <alloca.h>
#ifndef SECTION
# define SECTION
#endif
#ifndef NO__CONST
const mp_no __mpone = { 1, { 1.0, 1.0 } };
const mp_no __mptwo = { 1, { 1.0, 2.0 } };
#endif
#ifndef NO___ACR
/* Compare mantissa of two multiple precision numbers regardless of the sign
and exponent of the numbers. */
static int
mcr (const mp_no *x, const mp_no *y, int p)
{
long i;
long p2 = p;
for (i = 1; i <= p2; i++)
{
if (X[i] == Y[i])
continue;
else if (X[i] > Y[i])
return 1;
else
return -1;
}
return 0;
}
/* Compare the absolute values of two multiple precision numbers. */
int
__acr (const mp_no *x, const mp_no *y, int p)
{
long i;
if (X[0] == 0)
{
if (Y[0] == 0)
i = 0;
else
i = -1;
}
else if (Y[0] == 0)
i = 1;
else
{
if (EX > EY)
i = 1;
else if (EX < EY)
i = -1;
else
i = mcr (x, y, p);
}
return i;
}
#endif
#ifndef NO___CPY
/* Copy multiple precision number X into Y. They could be the same
number. */
void
__cpy (const mp_no *x, mp_no *y, int p)
{
long i;
EY = EX;
for (i = 0; i <= p; i++)
Y[i] = X[i];
}
#endif
#ifndef NO___MP_DBL
/* Convert a multiple precision number *X into a double precision
number *Y, normalized case (|x| >= 2**(-1022))). X has precision
P, which is positive. */
static void
norm (const mp_no *x, double *y, int p)
{
# define R RADIXI
long i;
double c;
mantissa_t a, u, v, z[5];
if (p < 5)
{
if (p == 1)
c = X[1];
else if (p == 2)
c = X[1] + R * X[2];
else if (p == 3)
c = X[1] + R * (X[2] + R * X[3]);
else /* p == 4. */
c = (X[1] + R * X[2]) + R * R * (X[3] + R * X[4]);
}
else
{
for (a = 1, z[1] = X[1]; z[1] < TWO23; )
{
a *= 2;
z[1] *= 2;
}
for (i = 2; i < 5; i++)
{
mantissa_store_t d, r;
d = X[i] * (mantissa_store_t) a;
DIV_RADIX (d, r);
z[i] = r;
z[i - 1] += d;
}
u = ALIGN_DOWN_TO (z[3], TWO19);
v = z[3] - u;
if (v == TWO18)
{
if (z[4] == 0)
{
for (i = 5; i <= p; i++)
{
if (X[i] == 0)
continue;
else
{
z[3] += 1;
break;
}
}
}
else
z[3] += 1;
}
c = (z[1] + R * (z[2] + R * z[3])) / a;
}
c *= X[0];
for (i = 1; i < EX; i++)
c *= RADIX;
for (i = 1; i > EX; i--)
c *= RADIXI;
*y = c;
# undef R
}
/* Convert a multiple precision number *X into a double precision
number *Y, Denormal case (|x| < 2**(-1022))). */
static void
denorm (const mp_no *x, double *y, int p)
{
long i, k;
long p2 = p;
double c;
mantissa_t u, z[5];
# define R RADIXI
if (EX < -44 || (EX == -44 && X[1] < TWO5))
{
*y = 0;
return;
}
if (p2 == 1)
{
if (EX == -42)
{
z[1] = X[1] + TWO10;
z[2] = 0;
z[3] = 0;
k = 3;
}
else if (EX == -43)
{
z[1] = TWO10;
z[2] = X[1];
z[3] = 0;
k = 2;
}
else
{
z[1] = TWO10;
z[2] = 0;
z[3] = X[1];
k = 1;
}
}
else if (p2 == 2)
{
if (EX == -42)
{
z[1] = X[1] + TWO10;
z[2] = X[2];
z[3] = 0;
k = 3;
}
else if (EX == -43)
{
z[1] = TWO10;
z[2] = X[1];
z[3] = X[2];
k = 2;
}
else
{
z[1] = TWO10;
z[2] = 0;
z[3] = X[1];
k = 1;
}
}
else
{
if (EX == -42)
{
z[1] = X[1] + TWO10;
z[2] = X[2];
k = 3;
}
else if (EX == -43)
{
z[1] = TWO10;
z[2] = X[1];
k = 2;
}
else
{
z[1] = TWO10;
z[2] = 0;
k = 1;
}
z[3] = X[k];
}
u = ALIGN_DOWN_TO (z[3], TWO5);
if (u == z[3])
{
for (i = k + 1; i <= p2; i++)
{
if (X[i] == 0)
continue;
else
{
z[3] += 1;
break;
}
}
}
c = X[0] * ((z[1] + R * (z[2] + R * z[3])) - TWO10);
*y = c * TWOM1032;
# undef R
}
/* Convert multiple precision number *X into double precision number *Y. The
result is correctly rounded to the nearest/even. */
void
__mp_dbl (const mp_no *x, double *y, int p)
{
if (X[0] == 0)
{
*y = 0;
return;
}
if (__glibc_likely (EX > -42 || (EX == -42 && X[1] >= TWO10)))
norm (x, y, p);
else
denorm (x, y, p);
}
#endif
/* Get the multiple precision equivalent of X into *Y. If the precision is too
small, the result is truncated. */
void
SECTION
__dbl_mp (double x, mp_no *y, int p)
{
long i, n;
long p2 = p;
/* Sign. */
if (x == 0)
{
Y[0] = 0;
return;
}
else if (x > 0)
Y[0] = 1;
else
{
Y[0] = -1;
x = -x;
}
/* Exponent. */
for (EY = 1; x >= RADIX; EY += 1)
x *= RADIXI;
for (; x < 1; EY -= 1)
x *= RADIX;
/* Digits. */
n = MIN (p2, 4);
for (i = 1; i <= n; i++)
{
INTEGER_OF (x, Y[i]);
x *= RADIX;
}
for (; i <= p2; i++)
Y[i] = 0;
}
/* Add magnitudes of *X and *Y assuming that abs (*X) >= abs (*Y) > 0. The
sign of the sum *Z is not changed. X and Y may overlap but not X and Z or
Y and Z. No guard digit is used. The result equals the exact sum,
truncated. */
static void
SECTION
add_magnitudes (const mp_no *x, const mp_no *y, mp_no *z, int p)
{
long i, j, k;
long p2 = p;
mantissa_t zk;
EZ = EX;
i = p2;
j = p2 + EY - EX;
k = p2 + 1;
if (__glibc_unlikely (j < 1))
{
__cpy (x, z, p);
return;
}
zk = 0;
for (; j > 0; i--, j--)
{
zk += X[i] + Y[j];
if (zk >= RADIX)
{
Z[k--] = zk - RADIX;
zk = 1;
}
else
{
Z[k--] = zk;
zk = 0;
}
}
for (; i > 0; i--)
{
zk += X[i];
if (zk >= RADIX)
{
Z[k--] = zk - RADIX;
zk = 1;
}
else
{
Z[k--] = zk;
zk = 0;
}
}
if (zk == 0)
{
for (i = 1; i <= p2; i++)
Z[i] = Z[i + 1];
}
else
{
Z[1] = zk;
EZ += 1;
}
}
/* Subtract the magnitudes of *X and *Y assuming that abs (*x) > abs (*y) > 0.
The sign of the difference *Z is not changed. X and Y may overlap but not X
and Z or Y and Z. One guard digit is used. The error is less than one
ULP. */
static void
SECTION
sub_magnitudes (const mp_no *x, const mp_no *y, mp_no *z, int p)
{
long i, j, k;
long p2 = p;
mantissa_t zk;
EZ = EX;
i = p2;
j = p2 + EY - EX;
k = p2;
/* Y is too small compared to X, copy X over to the result. */
if (__glibc_unlikely (j < 1))
{
__cpy (x, z, p);
return;
}
/* The relevant least significant digit in Y is non-zero, so we factor it in
to enhance accuracy. */
if (j < p2 && Y[j + 1] > 0)
{
Z[k + 1] = RADIX - Y[j + 1];
zk = -1;
}
else
zk = Z[k + 1] = 0;
/* Subtract and borrow. */
for (; j > 0; i--, j--)
{
zk += (X[i] - Y[j]);
if (zk < 0)
{
Z[k--] = zk + RADIX;
zk = -1;
}
else
{
Z[k--] = zk;
zk = 0;
}
}
/* We're done with digits from Y, so it's just digits in X. */
for (; i > 0; i--)
{
zk += X[i];
if (zk < 0)
{
Z[k--] = zk + RADIX;
zk = -1;
}
else
{
Z[k--] = zk;
zk = 0;
}
}
/* Normalize. */
for (i = 1; Z[i] == 0; i++)
;
EZ = EZ - i + 1;
for (k = 1; i <= p2 + 1; )
Z[k++] = Z[i++];
for (; k <= p2; )
Z[k++] = 0;
}
/* Add *X and *Y and store the result in *Z. X and Y may overlap, but not X
and Z or Y and Z. One guard digit is used. The error is less than one
ULP. */
void
SECTION
__add (const mp_no *x, const mp_no *y, mp_no *z, int p)
{
int n;
if (X[0] == 0)
{
__cpy (y, z, p);
return;
}
else if (Y[0] == 0)
{
__cpy (x, z, p);
return;
}
if (X[0] == Y[0])
{
if (__acr (x, y, p) > 0)
{
add_magnitudes (x, y, z, p);
Z[0] = X[0];
}
else
{
add_magnitudes (y, x, z, p);
Z[0] = Y[0];
}
}
else
{
if ((n = __acr (x, y, p)) == 1)
{
sub_magnitudes (x, y, z, p);
Z[0] = X[0];
}
else if (n == -1)
{
sub_magnitudes (y, x, z, p);
Z[0] = Y[0];
}
else
Z[0] = 0;
}
}
/* Subtract *Y from *X and return the result in *Z. X and Y may overlap but
not X and Z or Y and Z. One guard digit is used. The error is less than
one ULP. */
void
SECTION
__sub (const mp_no *x, const mp_no *y, mp_no *z, int p)
{
int n;
if (X[0] == 0)
{
__cpy (y, z, p);
Z[0] = -Z[0];
return;
}
else if (Y[0] == 0)
{
__cpy (x, z, p);
return;
}
if (X[0] != Y[0])
{
if (__acr (x, y, p) > 0)
{
add_magnitudes (x, y, z, p);
Z[0] = X[0];
}
else
{
add_magnitudes (y, x, z, p);
Z[0] = -Y[0];
}
}
else
{
if ((n = __acr (x, y, p)) == 1)
{
sub_magnitudes (x, y, z, p);
Z[0] = X[0];
}
else if (n == -1)
{
sub_magnitudes (y, x, z, p);
Z[0] = -Y[0];
}
else
Z[0] = 0;
}
}
#ifndef NO__MUL
/* Multiply *X and *Y and store result in *Z. X and Y may overlap but not X
and Z or Y and Z. For P in [1, 2, 3], the exact result is truncated to P
digits. In case P > 3 the error is bounded by 1.001 ULP. */
void
SECTION
__mul (const mp_no *x, const mp_no *y, mp_no *z, int p)
{
long i, j, k, ip, ip2;
long p2 = p;
mantissa_store_t zk;
const mp_no *a;
mantissa_store_t *diag;
/* Is z=0? */
if (__glibc_unlikely (X[0] * Y[0] == 0))
{
Z[0] = 0;
return;
}
/* We need not iterate through all X's and Y's since it's pointless to
multiply zeroes. Here, both are zero... */
for (ip2 = p2; ip2 > 0; ip2--)
if (X[ip2] != 0 || Y[ip2] != 0)
break;
a = X[ip2] != 0 ? y : x;
/* ... and here, at least one of them is still zero. */
for (ip = ip2; ip > 0; ip--)
if (a->d[ip] != 0)
break;
/* The product looks like this for p = 3 (as an example):
a1 a2 a3
x b1 b2 b3
-----------------------------
a1*b3 a2*b3 a3*b3
a1*b2 a2*b2 a3*b2
a1*b1 a2*b1 a3*b1
So our K needs to ideally be P*2, but we're limiting ourselves to P + 3
for P >= 3. We compute the above digits in two parts; the last P-1
digits and then the first P digits. The last P-1 digits are a sum of
products of the input digits from P to P-k where K is 0 for the least
significant digit and increases as we go towards the left. The product
term is of the form X[k]*X[P-k] as can be seen in the above example.
The first P digits are also a sum of products with the same product term,
except that the sum is from 1 to k. This is also evident from the above
example.
Another thing that becomes evident is that only the most significant
ip+ip2 digits of the result are non-zero, where ip and ip2 are the
'internal precision' of the input numbers, i.e. digits after ip and ip2
are all 0. */
k = (__glibc_unlikely (p2 < 3)) ? p2 + p2 : p2 + 3;
while (k > ip + ip2 + 1)
Z[k--] = 0;
zk = 0;
/* Precompute sums of diagonal elements so that we can directly use them
later. See the next comment to know we why need them. */
diag = alloca (k * sizeof (mantissa_store_t));
mantissa_store_t d = 0;
for (i = 1; i <= ip; i++)
{
d += X[i] * (mantissa_store_t) Y[i];
diag[i] = d;
}
while (i < k)
diag[i++] = d;
while (k > p2)
{
long lim = k / 2;
if (k % 2 == 0)
/* We want to add this only once, but since we subtract it in the sum
of products above, we add twice. */
zk += 2 * X[lim] * (mantissa_store_t) Y[lim];
for (i = k - p2, j = p2; i < j; i++, j--)
zk += (X[i] + X[j]) * (mantissa_store_t) (Y[i] + Y[j]);
zk -= diag[k - 1];
DIV_RADIX (zk, Z[k]);
k--;
}
/* The real deal. Mantissa digit Z[k] is the sum of all X[i] * Y[j] where i
goes from 1 -> k - 1 and j goes the same range in reverse. To reduce the
number of multiplications, we halve the range and if k is an even number,
add the diagonal element X[k/2]Y[k/2]. Through the half range, we compute
X[i] * Y[j] as (X[i] + X[j]) * (Y[i] + Y[j]) - X[i] * Y[i] - X[j] * Y[j].
This reduction tells us that we're summing two things, the first term
through the half range and the negative of the sum of the product of all
terms of X and Y in the full range. i.e.
SUM(X[i] * Y[i]) for k terms. This is precalculated above for each k in
a single loop so that it completes in O(n) time and can hence be directly
used in the loop below. */
while (k > 1)
{
long lim = k / 2;
if (k % 2 == 0)
/* We want to add this only once, but since we subtract it in the sum
of products above, we add twice. */
zk += 2 * X[lim] * (mantissa_store_t) Y[lim];
for (i = 1, j = k - 1; i < j; i++, j--)
zk += (X[i] + X[j]) * (mantissa_store_t) (Y[i] + Y[j]);
zk -= diag[k - 1];
DIV_RADIX (zk, Z[k]);
k--;
}
Z[k] = zk;
/* Get the exponent sum into an intermediate variable. This is a subtle
optimization, where given enough registers, all operations on the exponent
happen in registers and the result is written out only once into EZ. */
int e = EX + EY;
/* Is there a carry beyond the most significant digit? */
if (__glibc_unlikely (Z[1] == 0))
{
for (i = 1; i <= p2; i++)
Z[i] = Z[i + 1];
e--;
}
EZ = e;
Z[0] = X[0] * Y[0];
}
#endif
#ifndef NO__SQR
/* Square *X and store result in *Y. X and Y may not overlap. For P in
[1, 2, 3], the exact result is truncated to P digits. In case P > 3 the
error is bounded by 1.001 ULP. This is a faster special case of
multiplication. */
void
SECTION
__sqr (const mp_no *x, mp_no *y, int p)
{
long i, j, k, ip;
mantissa_store_t yk;
/* Is z=0? */
if (__glibc_unlikely (X[0] == 0))
{
Y[0] = 0;
return;
}
/* We need not iterate through all X's since it's pointless to
multiply zeroes. */
for (ip = p; ip > 0; ip--)
if (X[ip] != 0)
break;
k = (__glibc_unlikely (p < 3)) ? p + p : p + 3;
while (k > 2 * ip + 1)
Y[k--] = 0;
yk = 0;
while (k > p)
{
mantissa_store_t yk2 = 0;
long lim = k / 2;
if (k % 2 == 0)
yk += X[lim] * (mantissa_store_t) X[lim];
/* In __mul, this loop (and the one within the next while loop) run
between a range to calculate the mantissa as follows:
Z[k] = X[k] * Y[n] + X[k+1] * Y[n-1] ... + X[n-1] * Y[k+1]
+ X[n] * Y[k]
For X == Y, we can get away with summing halfway and doubling the
result. For cases where the range size is even, the mid-point needs
to be added separately (above). */
for (i = k - p, j = p; i < j; i++, j--)
yk2 += X[i] * (mantissa_store_t) X[j];
yk += 2 * yk2;
DIV_RADIX (yk, Y[k]);
k--;
}
while (k > 1)
{
mantissa_store_t yk2 = 0;
long lim = k / 2;
if (k % 2 == 0)
yk += X[lim] * (mantissa_store_t) X[lim];
/* Likewise for this loop. */
for (i = 1, j = k - 1; i < j; i++, j--)
yk2 += X[i] * (mantissa_store_t) X[j];
yk += 2 * yk2;
DIV_RADIX (yk, Y[k]);
k--;
}
Y[k] = yk;
/* Squares are always positive. */
Y[0] = 1;
/* Get the exponent sum into an intermediate variable. This is a subtle
optimization, where given enough registers, all operations on the exponent
happen in registers and the result is written out only once into EZ. */
int e = EX * 2;
/* Is there a carry beyond the most significant digit? */
if (__glibc_unlikely (Y[1] == 0))
{
for (i = 1; i <= p; i++)
Y[i] = Y[i + 1];
e--;
}
EY = e;
}
#endif
/* Invert *X and store in *Y. Relative error bound:
- For P = 2: 1.001 * R ^ (1 - P)
- For P = 3: 1.063 * R ^ (1 - P)
- For P > 3: 2.001 * R ^ (1 - P)
*X = 0 is not permissible. */
static void
SECTION
__inv (const mp_no *x, mp_no *y, int p)
{
long i;
double t;
mp_no z, w;
static const int np1[] =
{ 0, 0, 0, 0, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4
};
__cpy (x, &z, p);
z.e = 0;
__mp_dbl (&z, &t, p);
t = 1 / t;
__dbl_mp (t, y, p);
EY -= EX;
for (i = 0; i < np1[p]; i++)
{
__cpy (y, &w, p);
__mul (x, &w, y, p);
__sub (&__mptwo, y, &z, p);
__mul (&w, &z, y, p);
}
}
/* Divide *X by *Y and store result in *Z. X and Y may overlap but not X and Z
or Y and Z. Relative error bound:
- For P = 2: 2.001 * R ^ (1 - P)
- For P = 3: 2.063 * R ^ (1 - P)
- For P > 3: 3.001 * R ^ (1 - P)
*X = 0 is not permissible. */
void
SECTION
__dvd (const mp_no *x, const mp_no *y, mp_no *z, int p)
{
mp_no w;
if (X[0] == 0)
Z[0] = 0;
else
{
__inv (y, &w, p);
__mul (x, &w, z, p);
}
}
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