From e3dcaaf0d9e206b0acd9597622c6d3d423cb5ed5 Mon Sep 17 00:00:00 2001
From: vlefevre <vlefevre@280ebfd0-de03-0410-8827-d642c229c3f4>
Date: Thu, 26 Mar 2020 17:09:28 +0000
Subject: [src] Portability fixes. Avoid a potential integer overflow with huge
 precisions. (merged changesets r13792-13793,13795 from the trunk)

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/branches/4.0@13828 280ebfd0-de03-0410-8827-d642c229c3f4
---
 src/agm.c  |  2 +-
 src/pow.c  | 11 +++++++----
 src/rem1.c |  6 ++++--
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/src/agm.c b/src/agm.c
index faa23d266..4a39c2e44 100644
--- a/src/agm.c
+++ b/src/agm.c
@@ -220,7 +220,7 @@ mpfr_agm (mpfr_ptr r, mpfr_srcptr op2, mpfr_srcptr op1, mpfr_rnd_t rnd_mode)
           mpfr_add (vf, u, v, MPFR_RNDN);  /* No overflow? */
           mpfr_div_2ui (vf, vf, 1, MPFR_RNDN);
           /* See proof in algorithms.tex */
-          if (4*eq > p)
+          if (eq > p / 4)
             {
               mpfr_t w;
               MPFR_BLOCK_DECL (flags3);
diff --git a/src/pow.c b/src/pow.c
index 0063c0041..9fec8025e 100644
--- a/src/pow.c
+++ b/src/pow.c
@@ -34,8 +34,7 @@ mpfr_pow_is_exact (mpfr_ptr z, mpfr_srcptr x, mpfr_srcptr y,
                    mpfr_rnd_t rnd_mode, int *inexact)
 {
   mpz_t a, c;
-  mpfr_exp_t d, b;
-  unsigned long i;
+  mpfr_exp_t d, b, i;
   int res;
 
   MPFR_ASSERTD (!MPFR_IS_SINGULAR (y));
@@ -48,7 +47,9 @@ mpfr_pow_is_exact (mpfr_ptr z, mpfr_srcptr x, mpfr_srcptr y,
   if (MPFR_IS_NEG (y))
     return 0; /* x is not a power of two => x^-y is not exact */
 
-  /* compute d such that y = c*2^d with c odd integer */
+  /* Compute d such that y = c*2^d with c odd integer.
+     Since c comes from a regular MPFR number, due to the constraints on the
+     exponent and the precision, there can be no integer overflow below. */
   mpz_init (c);
   d = mpfr_get_z_2exp (c, y);
   i = mpz_scan1 (c, 0);
@@ -58,7 +59,9 @@ mpfr_pow_is_exact (mpfr_ptr z, mpfr_srcptr x, mpfr_srcptr y,
   /* Since y is not an integer, d is necessarily < 0 */
   MPFR_ASSERTD (d < 0);
 
-  /* Compute a,b such that x=a*2^b */
+  /* Compute a,b such that x=a*2^b.
+     Since a comes from a regular MPFR number, due to the constrainst on the
+     exponent and the precision, there can be no integer overflow below. */
   mpz_init (a);
   b = mpfr_get_z_2exp (a, x);
   i = mpz_scan1 (a, 0);
diff --git a/src/rem1.c b/src/rem1.c
index 3a7173c24..0ac742749 100644
--- a/src/rem1.c
+++ b/src/rem1.c
@@ -100,9 +100,11 @@ mpfr_rem1 (mpfr_ptr rem, long *quo, mpfr_rnd_t rnd_q,
   mpz_abs (my, my);
   q_is_odd = 0;
 
-  /* divide my by 2^k if possible to make operations mod my easier */
+  /* Divide my by 2^k if possible to make operations mod my easier.
+     Since my comes from a regular MPFR number, due to the constraints on the
+     exponent and the precision, there can be no integer overflow below. */
   {
-    unsigned long k = mpz_scan1 (my, 0);
+    mpfr_exp_t k = mpz_scan1 (my, 0);
     ey += k;
     mpz_fdiv_q_2exp (my, my, k);
   }
-- 
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