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/* mpfr_sqrt -- square root of a floating-point number
Copyright 1999-2020 Free Software Foundation, Inc.
Contributed by the AriC and Caramba projects, INRIA.
This file is part of the GNU MPFR Library.
The GNU MPFR 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 3 of the License, or (at your
option) any later version.
The GNU MPFR 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 the GNU MPFR Library; see the file COPYING.LESSER. If not, see
https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
#define MPFR_NEED_LONGLONG_H
#include "mpfr-impl.h"
#if !defined(MPFR_GENERIC_ABI) && GMP_NUMB_BITS == 64
#include "invsqrt_limb.h"
/* Put in rp[1]*2^64+rp[0] an approximation of floor(sqrt(2^128*n)),
with 2^126 <= n := np[1]*2^64 + np[0] < 2^128. We have:
{rp, 2} - 4 <= floor(sqrt(2^128*n)) <= {rp, 2} + 26. */
static void
mpfr_sqrt2_approx (mpfr_limb_ptr rp, mpfr_limb_srcptr np)
{
mp_limb_t x, r1, r0, h, l;
__gmpfr_sqrt_limb (r1, h, l, x, np[1]);
/* now r1 = floor(sqrt(2^64*n1)) and h:l = 2^64*n1 - r1^2 with h:l <= 2*r1,
thus h <= 1, and x is an approximation of 2^96/sqrt(np[1])-2^64 */
l += np[0];
h += (l < np[0]);
/* now 2^64*n1 + n0 - r1^2 = 2^64*h + l with h <= 2 */
/* divide by 2 */
l = (h << 63) | (l >> 1);
h = h >> 1;
/* now h <= 1 */
/* now add (2^64+x) * (h*2^64+l) / 2^64 to [r1*2^64, 0] */
umul_hi (r0, x, l); /* x * l */
r0 += l;
r1 += h + (r0 < l); /* now we have added 2^64 * (h*2^64+l) */
if (h)
{
r0 += x;
r1 += (r0 < x); /* add x */
}
MPFR_ASSERTD(r1 & MPFR_LIMB_HIGHBIT);
rp[0] = r0;
rp[1] = r1;
}
/* Special code for prec(r) = prec(u) < GMP_NUMB_BITS. We cannot have
prec(u) = GMP_NUMB_BITS here, since when the exponent of u is odd,
we need to shift u by one bit to the right without losing any bit.
Assumes GMP_NUMB_BITS = 64. */
static int
mpfr_sqrt1 (mpfr_ptr r, mpfr_srcptr u, mpfr_rnd_t rnd_mode)
{
mpfr_prec_t p = MPFR_GET_PREC(r);
mpfr_prec_t exp_u = MPFR_EXP(u), exp_r, sh = GMP_NUMB_BITS - p;
mp_limb_t u0, r0, rb, sb, mask = MPFR_LIMB_MASK(sh);
mpfr_limb_ptr rp = MPFR_MANT(r);
MPFR_STAT_STATIC_ASSERT (GMP_NUMB_BITS == 64);
/* first make the exponent even */
u0 = MPFR_MANT(u)[0];
if (((unsigned int) exp_u & 1) != 0)
{
u0 >>= 1;
exp_u ++;
}
MPFR_ASSERTD (((unsigned int) exp_u & 1) == 0);
exp_r = exp_u / 2;
/* then compute an approximation of the integer square root of
u0*2^GMP_NUMB_BITS */
__gmpfr_sqrt_limb_approx (r0, u0);
sb = 1; /* when we can round correctly with the approximation, the sticky bit
is non-zero */
/* the exact square root is in [r0, r0 + 7] */
if (MPFR_UNLIKELY(((r0 + 7) & (mask >> 1)) <= 7))
{
/* We should ensure r0 has its most significant bit set.
Since r0 <= sqrt(2^64*u0) <= r0 + 7, as soon as sqrt(2^64*u0)>=2^63+7,
which happens for u0>=2^62+8, then r0 >= 2^63.
It thus remains to check that for 2^62 <= u0 <= 2^62+7,
__gmpfr_sqrt_limb_approx (r0, u0) gives r0 >= 2^63, which is indeed
the case:
u0=4611686018427387904 r0=9223372036854775808
u0=4611686018427387905 r0=9223372036854775808
u0=4611686018427387906 r0=9223372036854775809
u0=4611686018427387907 r0=9223372036854775810
u0=4611686018427387908 r0=9223372036854775811
u0=4611686018427387909 r0=9223372036854775812
u0=4611686018427387910 r0=9223372036854775813
u0=4611686018427387911 r0=9223372036854775814 */
MPFR_ASSERTD(r0 >= MPFR_LIMB_HIGHBIT);
umul_ppmm (rb, sb, r0, r0);
sub_ddmmss (rb, sb, u0, 0, rb, sb);
/* for the exact square root, we should have 0 <= rb:sb <= 2*r0 */
while (!(rb == 0 || (rb == 1 && sb <= 2 * r0)))
{
/* subtract 2*r0+1 from rb:sb: subtract r0 before incrementing r0,
then r0 after (which is r0+1) */
rb -= (sb < r0);
sb -= r0;
r0 ++;
rb -= (sb < r0);
sb -= r0;
}
/* now we should have rb*2^64 + sb <= 2*r0 */
MPFR_ASSERTD(rb == 0 || (rb == 1 && sb <= 2 * r0));
sb = rb | sb;
}
rb = r0 & (MPFR_LIMB_ONE << (sh - 1));
sb |= (r0 & mask) ^ rb;
rp[0] = r0 & ~mask;
/* rounding: sb = 0 implies rb = 0, since (rb,sb)=(1,0) is not possible */
MPFR_ASSERTD (rb == 0 || sb != 0);
/* Note: if 1 and 2 are in [emin,emax], no overflow nor underflow
is possible */
if (MPFR_UNLIKELY (exp_r > __gmpfr_emax))
return mpfr_overflow (r, rnd_mode, 1);
/* See comments in mpfr_div_1 */
if (MPFR_UNLIKELY (exp_r < __gmpfr_emin))
{
if (rnd_mode == MPFR_RNDN)
{
/* If (1-2^(-p-1))*2^(emin-1) <= sqrt(u) < 2^(emin-1),
then sqrt(u) would be rounded to 2^(emin-1) with unbounded
exponent range, and there would be no underflow.
But this case cannot happen if u has precision p.
Indeed, we would have:
(1-2^(-p-1))^2*2^(2*emin-2) <= u < 2^(2*emin-2), i.e.,
(1-2^(-p)+2^(-2p-2))*2^(2*emin-2) <= u < 2^(2*emin-2),
and there is no p-bit number in that interval. */
/* If the result is <= 0.5^2^(emin-1), we should round to 0. */
if (exp_r < __gmpfr_emin - 1 ||
(rp[0] == MPFR_LIMB_HIGHBIT && sb == 0))
rnd_mode = MPFR_RNDZ;
}
else if (MPFR_IS_LIKE_RNDA(rnd_mode, 0))
{
if (exp_r == __gmpfr_emin - 1 &&
rp[0] == ~mask &&
(rb | sb) != 0)
goto rounding; /* no underflow */
}
return mpfr_underflow (r, rnd_mode, 1);
}
rounding:
MPFR_EXP (r) = exp_r;
if (sb == 0 /* implies rb = 0 */ || rnd_mode == MPFR_RNDF)
{
MPFR_ASSERTD (rb == 0 || rnd_mode == MPFR_RNDF);
MPFR_ASSERTD(exp_r >= __gmpfr_emin);
MPFR_ASSERTD(exp_r <= __gmpfr_emax);
MPFR_RET (0);
}
else if (rnd_mode == MPFR_RNDN)
{
/* since sb <> 0, only rb is needed to decide how to round, and the exact
middle is not possible */
if (rb == 0)
goto truncate;
else
goto add_one_ulp;
}
else if (MPFR_IS_LIKE_RNDZ(rnd_mode, 0))
{
truncate:
MPFR_ASSERTD(exp_r >= __gmpfr_emin);
MPFR_ASSERTD(exp_r <= __gmpfr_emax);
MPFR_RET(-1);
}
else /* round away from zero */
{
add_one_ulp:
rp[0] += MPFR_LIMB_ONE << sh;
if (rp[0] == 0)
{
rp[0] = MPFR_LIMB_HIGHBIT;
if (MPFR_UNLIKELY(exp_r + 1 > __gmpfr_emax))
return mpfr_overflow (r, rnd_mode, 1);
MPFR_ASSERTD(exp_r + 1 <= __gmpfr_emax);
MPFR_ASSERTD(exp_r + 1 >= __gmpfr_emin);
MPFR_SET_EXP (r, exp_r + 1);
}
MPFR_RET(1);
}
}
/* Special code for prec(r) = prec(u) = GMP_NUMB_BITS. */
static int
mpfr_sqrt1n (mpfr_ptr r, mpfr_srcptr u, mpfr_rnd_t rnd_mode)
{
mpfr_prec_t exp_u = MPFR_EXP(u), exp_r;
mp_limb_t u0, r0, rb, sb, low;
mpfr_limb_ptr rp = MPFR_MANT(r);
MPFR_STAT_STATIC_ASSERT (GMP_NUMB_BITS == 64);
MPFR_ASSERTD(MPFR_PREC(r) == GMP_NUMB_BITS);
MPFR_ASSERTD(MPFR_PREC(u) <= GMP_NUMB_BITS);
/* first make the exponent even */
u0 = MPFR_MANT(u)[0];
if (((unsigned int) exp_u & 1) != 0)
{
low = u0 << (GMP_NUMB_BITS - 1);
u0 >>= 1;
exp_u ++;
}
else
low = 0; /* low part of u0 */
MPFR_ASSERTD (((unsigned int) exp_u & 1) == 0);
exp_r = exp_u / 2;
/* then compute an approximation of the integer square root of
u0*2^GMP_NUMB_BITS */
__gmpfr_sqrt_limb_approx (r0, u0);
/* the exact square root is in [r0, r0 + 7] */
/* As shown in mpfr_sqrt1 above, r0 has its most significant bit set */
MPFR_ASSERTD(r0 >= MPFR_LIMB_HIGHBIT);
umul_ppmm (rb, sb, r0, r0);
sub_ddmmss (rb, sb, u0, low, rb, sb);
/* for the exact square root, we should have 0 <= rb:sb <= 2*r0 */
while (!(rb == 0 || (rb == 1 && sb <= 2 * r0)))
{
/* subtract 2*r0+1 from rb:sb: subtract r0 before incrementing r0,
then r0 after (which is r0+1) */
rb -= (sb < r0);
sb -= r0;
r0 ++;
rb -= (sb < r0);
sb -= r0;
}
/* now we have u0*2^64+low = r0^2 + rb*2^64+sb, with rb*2^64+sb <= 2*r0 */
MPFR_ASSERTD(rb == 0 || (rb == 1 && sb <= 2 * r0));
/* We can't have the middle case u0*2^64 = (r0 + 1/2)^2 since
(r0 + 1/2)^2 is not an integer.
We thus rb = 1 whenever u0*2^64 > (r0 + 1/2)^2, thus rb*2^64 + sb > r0
and the sticky bit is always 1, unless we had rb = sb = 0. */
rb = rb || (sb > r0);
sb = rb | sb;
rp[0] = r0;
/* rounding */
/* Note: if 1 and 2 are in [emin,emax], no overflow nor underflow
is possible */
if (MPFR_UNLIKELY (exp_r > __gmpfr_emax))
return mpfr_overflow (r, rnd_mode, 1);
/* See comments in mpfr_div_1 */
if (MPFR_UNLIKELY (exp_r < __gmpfr_emin))
{
if (rnd_mode == MPFR_RNDN)
{
/* the case rp[0] = 111...111 and rb = 1 cannot happen, since it
would imply u0 >= (2^64-1/2)^2/2^64 thus u0 >= 2^64 */
if (exp_r < __gmpfr_emin - 1 ||
(rp[0] == MPFR_LIMB_HIGHBIT && sb == 0))
rnd_mode = MPFR_RNDZ;
}
else if (MPFR_IS_LIKE_RNDA(rnd_mode, 0))
{
if (exp_r == __gmpfr_emin - 1 &&
rp[0] == MPFR_LIMB_MAX &&
(rb | sb) != 0)
goto rounding; /* no underflow */
}
return mpfr_underflow (r, rnd_mode, 1);
}
/* sb = 0 can only occur when the square root is exact, i.e., rb = 0 */
rounding:
MPFR_EXP (r) = exp_r;
if (sb == 0 /* implies rb = 0 */ || rnd_mode == MPFR_RNDF)
{
MPFR_ASSERTD(exp_r >= __gmpfr_emin);
MPFR_ASSERTD(exp_r <= __gmpfr_emax);
MPFR_RET (0);
}
else if (rnd_mode == MPFR_RNDN)
{
/* we can't have sb = 0, thus rb is enough */
if (rb == 0)
goto truncate;
else
goto add_one_ulp;
}
else if (MPFR_IS_LIKE_RNDZ(rnd_mode, 0))
{
truncate:
MPFR_ASSERTD(exp_r >= __gmpfr_emin);
MPFR_ASSERTD(exp_r <= __gmpfr_emax);
MPFR_RET(-1);
}
else /* round away from zero */
{
add_one_ulp:
rp[0] += MPFR_LIMB_ONE;
if (rp[0] == 0)
{
rp[0] = MPFR_LIMB_HIGHBIT;
if (MPFR_UNLIKELY(exp_r + 1 > __gmpfr_emax))
return mpfr_overflow (r, rnd_mode, 1);
MPFR_ASSERTD(exp_r + 1 <= __gmpfr_emax);
MPFR_ASSERTD(exp_r + 1 >= __gmpfr_emin);
MPFR_SET_EXP (r, exp_r + 1);
}
MPFR_RET(1);
}
}
/* Special code for GMP_NUMB_BITS < prec(r) = prec(u) < 2*GMP_NUMB_BITS.
Assumes GMP_NUMB_BITS=64. */
static int
mpfr_sqrt2 (mpfr_ptr r, mpfr_srcptr u, mpfr_rnd_t rnd_mode)
{
mpfr_prec_t p = MPFR_GET_PREC(r);
mpfr_limb_ptr up = MPFR_MANT(u), rp = MPFR_MANT(r);
mp_limb_t np[4], rb, sb, mask;
mpfr_prec_t exp_u = MPFR_EXP(u), exp_r, sh = 2 * GMP_NUMB_BITS - p;
MPFR_STAT_STATIC_ASSERT (GMP_NUMB_BITS == 64);
if (((unsigned int) exp_u & 1) != 0)
{
np[3] = up[1] >> 1;
np[2] = (up[1] << (GMP_NUMB_BITS - 1)) | (up[0] >> 1);
np[1] = up[0] << (GMP_NUMB_BITS - 1);
exp_u ++;
}
else
{
np[3] = up[1];
np[2] = up[0];
np[1] = 0;
}
exp_r = exp_u / 2;
mask = MPFR_LIMB_MASK(sh);
mpfr_sqrt2_approx (rp, np + 2);
/* with n = np[3]*2^64+np[2], we have:
{rp, 2} - 4 <= floor(sqrt(2^128*n)) <= {rp, 2} + 26, thus we can round
correctly except when the number formed by the last sh-1 bits
of rp[0] is in the range [-26, 4]. */
if (MPFR_LIKELY(((rp[0] + 26) & (mask >> 1)) > 30))
sb = 1;
else
{
mp_limb_t tp[4], h, l;
np[0] = 0;
mpn_sqr (tp, rp, 2);
/* since we know s - 26 <= r <= s + 4 and 0 <= n^2 - s <= 2*s, we have
-8*s-16 <= n - r^2 <= 54*s - 676, thus it suffices to compute
n - r^2 modulo 2^192 */
mpn_sub_n (tp, np, tp, 3);
/* invariant: h:l = 2 * {rp, 2}, with upper bit implicit */
h = (rp[1] << 1) | (rp[0] >> (GMP_NUMB_BITS - 1));
l = rp[0] << 1;
while ((mp_limb_signed_t) tp[2] < 0) /* approximation was too large */
{
/* subtract 1 to {rp, 2}, thus 2 to h:l */
h -= (l <= MPFR_LIMB_ONE);
l -= 2;
/* add (1:h:l)+1 to {tp,3} */
tp[0] += l + 1;
tp[1] += h + (tp[0] < l);
/* necessarily rp[1] has its most significant bit set */
tp[2] += MPFR_LIMB_ONE + (tp[1] < h || (tp[1] == h && tp[0] < l));
}
/* now tp[2] >= 0 */
/* now we want {tp, 4} <= 2 * {rp, 2}, which implies tp[2] <= 1 */
while (tp[2] > 1 || (tp[2] == 1 && tp[1] > h) ||
(tp[2] == 1 && tp[1] == h && tp[0] > l))
{
/* subtract (1:h:l)+1 from {tp,3} */
tp[2] -= MPFR_LIMB_ONE + (tp[1] < h || (tp[1] == h && tp[0] <= l));
tp[1] -= h + (tp[0] <= l);
tp[0] -= l + 1;
/* add 2 to h:l */
l += 2;
h += (l <= MPFR_LIMB_ONE);
}
/* restore {rp, 2} from h:l */
rp[1] = MPFR_LIMB_HIGHBIT | (h >> 1);
rp[0] = (h << (GMP_NUMB_BITS - 1)) | (l >> 1);
sb = tp[2] | tp[0] | tp[1];
}
rb = rp[0] & (MPFR_LIMB_ONE << (sh - 1));
sb |= (rp[0] & mask) ^ rb;
rp[0] = rp[0] & ~mask;
/* rounding */
if (MPFR_UNLIKELY (exp_r > __gmpfr_emax))
return mpfr_overflow (r, rnd_mode, 1);
/* See comments in mpfr_div_1 */
if (MPFR_UNLIKELY (exp_r < __gmpfr_emin))
{
if (rnd_mode == MPFR_RNDN)
{
if (exp_r < __gmpfr_emin - 1 || (rp[1] == MPFR_LIMB_HIGHBIT &&
rp[0] == MPFR_LIMB_ZERO && sb == 0))
rnd_mode = MPFR_RNDZ;
}
else if (MPFR_IS_LIKE_RNDA(rnd_mode, 0))
{
if (exp_r == __gmpfr_emin - 1 && (rp[1] == MPFR_LIMB_MAX &&
rp[0] == ~mask) && (rb | sb))
goto rounding; /* no underflow */
}
return mpfr_underflow (r, rnd_mode, 1);
}
rounding:
MPFR_EXP (r) = exp_r;
if (sb == 0 /* implies rb = 0 */ || rnd_mode == MPFR_RNDF)
{
MPFR_ASSERTD(exp_r >= __gmpfr_emin);
MPFR_ASSERTD(exp_r <= __gmpfr_emax);
MPFR_RET (0);
}
else if (rnd_mode == MPFR_RNDN)
{
/* since sb <> 0 now, only rb is needed */
if (rb == 0)
goto truncate;
else
goto add_one_ulp;
}
else if (MPFR_IS_LIKE_RNDZ(rnd_mode, 0))
{
truncate:
MPFR_ASSERTD(exp_r >= __gmpfr_emin);
MPFR_ASSERTD(exp_r <= __gmpfr_emax);
MPFR_RET(-1);
}
else /* round away from zero */
{
add_one_ulp:
rp[0] += MPFR_LIMB_ONE << sh;
rp[1] += rp[0] == 0;
if (rp[1] == 0)
{
rp[1] = MPFR_LIMB_HIGHBIT;
if (MPFR_UNLIKELY(exp_r + 1 > __gmpfr_emax))
return mpfr_overflow (r, rnd_mode, 1);
MPFR_ASSERTD(exp_r + 1 <= __gmpfr_emax);
MPFR_ASSERTD(exp_r + 1 >= __gmpfr_emin);
MPFR_SET_EXP (r, exp_r + 1);
}
MPFR_RET(1);
}
}
#endif /* !defined(MPFR_GENERIC_ABI) && GMP_NUMB_BITS == 64 */
int
mpfr_sqrt (mpfr_ptr r, mpfr_srcptr u, mpfr_rnd_t rnd_mode)
{
mp_size_t rsize; /* number of limbs of r (plus 1 if exact limb multiple) */
mp_size_t rrsize;
mp_size_t usize; /* number of limbs of u */
mp_size_t tsize; /* number of limbs of the sqrtrem remainder */
mp_size_t k;
mp_size_t l;
mpfr_limb_ptr rp, rp0;
mpfr_limb_ptr up;
mpfr_limb_ptr sp;
mp_limb_t sticky0; /* truncated part of input */
mp_limb_t sticky1; /* truncated part of rp[0] */
mp_limb_t sticky;
int odd_exp;
int sh; /* number of extra bits in rp[0] */
int inexact; /* return ternary flag */
mpfr_exp_t expr;
mpfr_prec_t rq = MPFR_GET_PREC (r);
MPFR_TMP_DECL(marker);
MPFR_LOG_FUNC
(("x[%Pu]=%.*Rg rnd=%d", mpfr_get_prec (u), mpfr_log_prec, u, rnd_mode),
("y[%Pu]=%.*Rg inexact=%d",
mpfr_get_prec (r), mpfr_log_prec, r, inexact));
if (MPFR_UNLIKELY(MPFR_IS_SINGULAR(u)))
{
if (MPFR_IS_NAN(u))
{
MPFR_SET_NAN(r);
MPFR_RET_NAN;
}
else if (MPFR_IS_ZERO(u))
{
/* 0+ or 0- */
MPFR_SET_SAME_SIGN(r, u);
MPFR_SET_ZERO(r);
MPFR_RET(0); /* zero is exact */
}
else
{
MPFR_ASSERTD(MPFR_IS_INF(u));
/* sqrt(-Inf) = NAN */
if (MPFR_IS_NEG(u))
{
MPFR_SET_NAN(r);
MPFR_RET_NAN;
}
MPFR_SET_POS(r);
MPFR_SET_INF(r);
MPFR_RET(0);
}
}
if (MPFR_UNLIKELY(MPFR_IS_NEG(u)))
{
MPFR_SET_NAN(r);
MPFR_RET_NAN;
}
MPFR_SET_POS(r);
#if !defined(MPFR_GENERIC_ABI) && GMP_NUMB_BITS == 64
{
mpfr_prec_t uq = MPFR_GET_PREC (u);
if (rq == uq)
{
if (rq < GMP_NUMB_BITS)
return mpfr_sqrt1 (r, u, rnd_mode);
if (GMP_NUMB_BITS < rq && rq < 2*GMP_NUMB_BITS)
return mpfr_sqrt2 (r, u, rnd_mode);
if (rq == GMP_NUMB_BITS)
return mpfr_sqrt1n (r, u, rnd_mode);
}
}
#endif
MPFR_TMP_MARK (marker);
MPFR_UNSIGNED_MINUS_MODULO (sh, rq);
if (sh == 0 && rnd_mode == MPFR_RNDN)
sh = GMP_NUMB_BITS; /* ugly case */
rsize = MPFR_LIMB_SIZE(r) + (sh == GMP_NUMB_BITS);
/* rsize is the number of limbs of r + 1 if exact limb multiple and rounding
to nearest, this is the number of wanted limbs for the square root */
rrsize = rsize + rsize;
usize = MPFR_LIMB_SIZE(u); /* number of limbs of u */
rp0 = MPFR_MANT(r);
rp = (sh < GMP_NUMB_BITS) ? rp0 : MPFR_TMP_LIMBS_ALLOC (rsize);
up = MPFR_MANT(u);
sticky0 = MPFR_LIMB_ZERO; /* truncated part of input */
sticky1 = MPFR_LIMB_ZERO; /* truncated part of rp[0] */
odd_exp = (unsigned int) MPFR_GET_EXP (u) & 1;
inexact = -1; /* return ternary flag */
sp = MPFR_TMP_LIMBS_ALLOC (rrsize);
/* copy the most significant limbs of u to {sp, rrsize} */
if (MPFR_LIKELY(usize <= rrsize)) /* in case r and u have the same precision,
we have indeed rrsize = 2 * usize */
{
k = rrsize - usize;
if (MPFR_LIKELY(k))
MPN_ZERO (sp, k);
if (odd_exp)
{
if (MPFR_LIKELY(k))
sp[k - 1] = mpn_rshift (sp + k, up, usize, 1);
else
sticky0 = mpn_rshift (sp, up, usize, 1);
}
else
MPN_COPY (sp + rrsize - usize, up, usize);
}
else /* usize > rrsize: truncate the input */
{
k = usize - rrsize;
if (odd_exp)
sticky0 = mpn_rshift (sp, up + k, rrsize, 1);
else
MPN_COPY (sp, up + k, rrsize);
l = k;
while (sticky0 == MPFR_LIMB_ZERO && l != 0)
sticky0 = up[--l];
}
/* sticky0 is non-zero iff the truncated part of the input is non-zero */
tsize = mpn_sqrtrem (rp, NULL, sp, rrsize);
/* a return value of zero in mpn_sqrtrem indicates a perfect square */
sticky = sticky0 || tsize != 0;
/* truncate low bits of rp[0] */
sticky1 = rp[0] & ((sh < GMP_NUMB_BITS) ? MPFR_LIMB_MASK(sh)
: MPFR_LIMB_MAX);
rp[0] -= sticky1;
sticky = sticky || sticky1;
expr = (MPFR_GET_EXP(u) + odd_exp) / 2; /* exact */
if (rnd_mode == MPFR_RNDZ || rnd_mode == MPFR_RNDD ||
sticky == MPFR_LIMB_ZERO)
{
inexact = (sticky == MPFR_LIMB_ZERO) ? 0 : -1;
goto truncate;
}
else if (rnd_mode == MPFR_RNDN)
{
/* if sh < GMP_NUMB_BITS, the round bit is bit (sh-1) of sticky1
and the sticky bit is formed by the low sh-1 bits from
sticky1, together with the sqrtrem remainder and sticky0. */
if (sh < GMP_NUMB_BITS)
{
if (sticky1 & (MPFR_LIMB_ONE << (sh - 1)))
{ /* round bit is set */
if (sticky1 == (MPFR_LIMB_ONE << (sh - 1)) && tsize == 0
&& sticky0 == 0)
goto even_rule;
else
goto add_one_ulp;
}
else /* round bit is zero */
goto truncate; /* with the default inexact=-1 */
}
else /* sh = GMP_NUMB_BITS: the round bit is the most significant bit
of rp[0], and the remaining GMP_NUMB_BITS-1 bits contribute to
the sticky bit */
{
if (sticky1 & MPFR_LIMB_HIGHBIT)
{ /* round bit is set */
if (sticky1 == MPFR_LIMB_HIGHBIT && tsize == 0 && sticky0 == 0)
goto even_rule;
else
goto add_one_ulp;
}
else /* round bit is zero */
goto truncate; /* with the default inexact=-1 */
}
}
else /* rnd_mode=GMP_RDNU, necessarily sticky <> 0, thus add 1 ulp */
goto add_one_ulp;
even_rule: /* has to set inexact */
if (sh < GMP_NUMB_BITS)
inexact = (rp[0] & (MPFR_LIMB_ONE << sh)) ? 1 : -1;
else
inexact = (rp[1] & MPFR_LIMB_ONE) ? 1 : -1;
if (inexact == -1)
goto truncate;
/* else go through add_one_ulp */
add_one_ulp:
inexact = 1; /* always here */
if (sh == GMP_NUMB_BITS)
{
rp ++;
rsize --;
sh = 0;
}
/* now rsize = MPFR_LIMB_SIZE(r) */
if (mpn_add_1 (rp0, rp, rsize, MPFR_LIMB_ONE << sh))
{
expr ++;
rp0[rsize - 1] = MPFR_LIMB_HIGHBIT;
}
goto end;
truncate: /* inexact = 0 or -1 */
if (sh == GMP_NUMB_BITS)
MPN_COPY (rp0, rp + 1, rsize - 1);
end:
/* Do not use MPFR_SET_EXP because the range has not been checked yet. */
MPFR_ASSERTN (expr >= MPFR_EMIN_MIN && expr <= MPFR_EMAX_MAX);
MPFR_EXP (r) = expr;
MPFR_TMP_FREE(marker);
return mpfr_check_range (r, inexact, rnd_mode);
}
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