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implement mag_sub_lower properly and test+document it

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This commit is contained in:
Fredrik Johansson 2014-11-06 14:29:56 +01:00
parent 2caaa4f230
commit 7d04c89504
8 changed files with 226 additions and 43 deletions
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2
acb_modular/eta_sum.c
View file

@ -45,8 +45,6 @@ acb_mul_approx(acb_t z, acb_t tmp1, acb_t tmp2, const acb_t x, const acb_t y, lo
}
}
void mag_sub_lower(mag_t z, const mag_t x, const mag_t y);
double mag_get_log2_d_approx(const mag_t x);
#define PENTAGONAL(N) ((((N)+2)/2) * ((3*(N)+5)/2)/2)

2
acb_modular/theta_sum.c
View file

@ -45,8 +45,6 @@ acb_mul_approx(acb_t z, acb_t tmp1, acb_t tmp2, const acb_t x, const acb_t y, lo
}
}
void mag_sub_lower(mag_t z, const mag_t x, const mag_t y);
double
mag_get_log2_d_approx(const mag_t x)
{

3
acb_poly/polylog_series.c
View file

@ -43,9 +43,6 @@ mag_log_ui(mag_t t, ulong n)
}
}
/* TODO: needs reimplementing */
void mag_sub_lower(mag_t z, const mag_t x, const mag_t y);
long
arb_get_si_lower(const arb_t x)
{

4
doc/source/mag.rst
View file

@ -220,6 +220,10 @@ Arithmetic
Sets *z* to a lower bound for `x + y`.
.. function:: void mag_sub_lower(mag_t z, const mag_t x, const mag_t y)
Sets *z* to a lower bound for `\max(x-y, 0)`.
Fast, unsafe arithmetic
-------------------------------------------------------------------------------

36
hypgeom/bound.c
View file

@ -207,42 +207,6 @@ hypgeom_term_bound(mag_t Tn, const mag_t TK, long K, long A, long B, int r, cons
mag_clear(num);
}
/* z = max(x-y, 0), rounding down [lower bound] */
void
mag_sub_lower(mag_t z, const mag_t x, const mag_t y)
{
if (mag_is_special(x) || mag_is_special(y))
{
if (mag_is_zero(y))
mag_set(z, x);
else if (mag_is_zero(x) || mag_is_inf(y))
mag_zero(z);
else
mag_inf(z);
}
else
{
fmpr_t t, u;
fmpr_init(t);
fmpr_init(u);
mag_get_fmpr(t, x);
mag_get_fmpr(u, y);
fmpr_sub(t, t, u, MAG_BITS, FMPR_RND_DOWN);
if (fmpr_sgn(t) <= 0)
mag_zero(z);
else /* XXX: exact? */
mag_set_fmpz_2exp_fmpz_lower(z, fmpr_manref(t), fmpr_expref(t));
fmpr_clear(t);
fmpr_clear(u);
}
}
long
hypgeom_bound(mag_t error, int r,
long A, long B, long K, const mag_t TK, const mag_t z, long tol_2exp)

2
mag.h
View file

@ -331,6 +331,8 @@ mag_mul_2exp_fmpz(mag_t z, const mag_t x, const fmpz_t y)
}
}
void mag_sub_lower(mag_t z, const mag_t x, const mag_t y);
/* Fast versions (no infs/nans, small exponents). Note that this
applies to outputs too! */

100
mag/sub_lower.c Normal file
View file

@ -0,0 +1,100 @@
/*=============================================================================
This file is part of ARB.
ARB is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
ARB 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with ARB; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2014 Fredrik Johansson
******************************************************************************/
#include "mag.h"
#include "arf.h"
void
mag_sub_lower(mag_t z, const mag_t x, const mag_t y)
{
if (mag_is_special(x) || mag_is_special(y))
{
if (mag_is_zero(y))
mag_set(z, x);
else if (mag_is_zero(x) || mag_is_inf(y))
mag_zero(z);
else
mag_inf(z);
}
else
{
long shift, fix;
shift = _fmpz_sub_small(MAG_EXPREF(x), MAG_EXPREF(y));
/* y > x */
if (shift < 0)
{
mag_zero(z);
}
else if (shift == 0)
{
if (MAG_MAN(y) >= MAG_MAN(x))
{
mag_zero(z);
}
else
{
MAG_MAN(z) = MAG_MAN(x) - MAG_MAN(y);
fix = MAG_BITS - FLINT_BIT_COUNT(MAG_MAN(z));
MAG_MAN(z) <<= fix;
_fmpz_add_fast(MAG_EXPREF(z), MAG_EXPREF(x), -fix);
}
}
else
{
if (shift <= MAG_BITS)
{
mp_limb_t c = MAG_MAN(x) - (MAG_MAN(y) >> shift) - 1;
/* too much cancellation -- compute precisely */
if (c < (1UL << (MAG_BITS - 4)))
{
arf_t t, u;
arf_init(t);
arf_init(u);
arf_set_mag(t, x);
arf_set_mag(u, y);
arf_sub(t, t, u, MAG_BITS, ARF_RND_DOWN);
arf_get_mag_lower(z, t);
arf_clear(t);
arf_clear(u);
return;
}
MAG_MAN(z) = c;
}
else
{
MAG_MAN(z) = MAG_MAN(x) - 1;
}
fix = MAG_BITS - FLINT_BIT_COUNT(MAG_MAN(z));
MAG_MAN(z) <<= fix;
_fmpz_add_fast(MAG_EXPREF(z), MAG_EXPREF(x), -fix);
}
}
}

120
mag/test/t-sub_lower.c Normal file
View file

@ -0,0 +1,120 @@
/*=============================================================================
This file is part of ARB.
ARB is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
ARB 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with ARB; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2014 Fredrik Johansson
******************************************************************************/
#include "mag.h"
int main()
{
long iter;
flint_rand_t state;
printf("sub_lower....");
fflush(stdout);
flint_randinit(state);
for (iter = 0; iter < 100000; iter++)
{
fmpr_t x, y, z, z2, w;
mag_t xb, yb, zb;
fmpr_init(x);
fmpr_init(y);
fmpr_init(z);
fmpr_init(z2);
fmpr_init(w);
mag_init(xb);
mag_init(yb);
mag_init(zb);
mag_randtest_special(xb, state, 100);
mag_randtest_special(yb, state, 100);
mag_get_fmpr(x, xb);
mag_get_fmpr(y, yb);
fmpr_sub(z2, x, y, 100, FMPR_RND_DOWN);
if (fmpr_sgn(z2) < 0)
fmpr_zero(z2);
fmpr_mul_ui(z, z2, 1023, MAG_BITS, FMPR_RND_DOWN);
fmpr_mul_2exp_si(z, z, -10);
mag_sub_lower(zb, xb, yb);
mag_get_fmpr(w, zb);
MAG_CHECK_BITS(xb)
MAG_CHECK_BITS(yb)
MAG_CHECK_BITS(zb)
if (!(fmpr_cmpabs(z, w) <= 0 && fmpr_cmpabs(w, z2) <= 0))
{
printf("FAIL\n\n");
printf("x = "); fmpr_print(x); printf("\n\n");
printf("y = "); fmpr_print(y); printf("\n\n");
printf("z = "); fmpr_print(z); printf("\n\n");
printf("w = "); fmpr_print(w); printf("\n\n");
abort();
}
if (n_randint(state, 2))
{
mag_sub_lower(xb, xb, yb);
if (!mag_equal(xb, zb))
{
printf("FAIL (aliasing 1)\n\n");
abort();
}
}
else
{
mag_sub_lower(yb, xb, yb);
if (!mag_equal(yb, zb))
{
printf("FAIL (aliasing 2)\n\n");
abort();
}
}
fmpr_clear(x);
fmpr_clear(y);
fmpr_clear(z);
fmpr_clear(z2);
fmpr_clear(w);
mag_clear(xb);
mag_clear(yb);
mag_clear(zb);
}
flint_randclear(state);
flint_cleanup();
printf("PASS\n");
return EXIT_SUCCESS;
}