From cab664d086ded9d356d2828325f6d62b3aecebdd Mon Sep 17 00:00:00 2001
From: jzmaddock <john@johnmaddock.co.uk>
Date: Sun, 26 Sep 2021 11:25:34 +0100
Subject: [PATCH] We need double_limb type for quotient calculation in Lehmers
 routine. Fixes https://github.com/boostorg/multiprecision/issues/370.

---
 include/boost/multiprecision/cpp_int/misc.hpp | 10 +++-----
 test/Jamfile.v2                               |  1 +
 test/git_issue_370.cpp                        | 25 +++++++++++++++++++
 3 files changed, 30 insertions(+), 6 deletions(-)
 create mode 100644 test/git_issue_370.cpp

diff --git a/include/boost/multiprecision/cpp_int/misc.hpp b/include/boost/multiprecision/cpp_int/misc.hpp
index cd9f29d2..2963bede 100644
--- a/include/boost/multiprecision/cpp_int/misc.hpp
+++ b/include/boost/multiprecision/cpp_int/misc.hpp
@@ -732,12 +732,10 @@ void eval_gcd_lehmer(cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Al
 // but that division is very slow.
 //
 // We begin with a specialized routine for division.
-// We know that u > v > ~limb_type(0), and therefore
-// that the result will fit into a single limb_type.
-// We also know that most of the time this is called the result will be 1.
+// We know that most of the time this is called the result will be 1.
 // For small limb counts, this almost doubles the performance of Lehmer's routine!
 //
-BOOST_FORCEINLINE void divide_subtract(limb_type& q, double_limb_type& u, const double_limb_type& v)
+BOOST_FORCEINLINE void divide_subtract(double_limb_type& q, double_limb_type& u, const double_limb_type& v)
 {
    BOOST_ASSERT(q == 1); // precondition on entry.
    u -= v;
@@ -746,7 +744,7 @@ BOOST_FORCEINLINE void divide_subtract(limb_type& q, double_limb_type& u, const
       u -= v;
       if (++q > 30)
       {
-         limb_type t = u / v;
+         double_limb_type t = u / v;
          u -= t * v;
          q += t;
       }
@@ -855,7 +853,7 @@ void eval_gcd_lehmer(cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Al
    //
    while (true)
    {
-      limb_type q = 1;
+      double_limb_type q = 1;
       double_limb_type tt = u;
       divide_subtract(q, u, v);
       std::swap(u, v);
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index a2861b81..58054adf 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -1112,6 +1112,7 @@ test-suite misc :
       [ run bug12039.cpp no_eh_support ]
       [ compile git_issue_30.cpp ]
       [ run git_issue_167.cpp ]
+      [ run git_issue_370.cpp ]
       [ run git_issue_175.cpp ]
       [ run git_issue_248.cpp ]
       [ run git_issue_265.cpp : : : [ check-target-builds ../config//has_mpfr : <source>gmp <source>mpfr : <build>no ] ]
diff --git a/test/git_issue_370.cpp b/test/git_issue_370.cpp
new file mode 100644
index 00000000..ae56a87b
--- /dev/null
+++ b/test/git_issue_370.cpp
@@ -0,0 +1,25 @@
+///////////////////////////////////////////////////////////////////////////////
+//  Copyright 2019 John Maddock. Distributed under the Boost
+//  Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/multiprecision/cpp_int.hpp>
+#include "test.hpp"
+
+int main()
+{
+   const boost::multiprecision::cpp_int a("500000000000000052504760255204421627079393309355027816932345132815919505535709229444276879024105562954502314530690391078574434507015318513443905076213688875017942541908041275407131568575177172639474548726709751235383681696449966404295647940685784470144122251803020020951078103818191513659921807053133698549053838430992170843235673537548059987539601671975279280846041564435631581262016246808786828637048154067265620710396778995313534536353760281048487250661054626168637371167135426013683337484254647996964562455566714879467026196409913165805735073230830136024016362543811769017875638974011487488573436");
+   const boost::multiprecision::cpp_int b("1500000000000000157514280765613264881238179928065083450797035398447758516607127688332830637072316688863506943592071173235723303521045955540331715228641066625053827625724123826221394705725531517918423646180129253706151045089349899212886943822057353410432366755409060062853234311454574540979765421159386595647161515292215193506006556519037965168192736708179557957863203557666055574947146355487693991882510747766220045897624670399027877365714431356466054500731862264092476764347207739651025585146903094168986610767496468412336047796468657032646893153521091155634158263410282629846280069312485301157888001");
+   const boost::multiprecision::cpp_int r = gcd(a, b);
+
+   if (a % r)
+      return 1;
+   if (b % r)
+      return 1;
+   if (gcd(a / r, b / r) != 1)
+      return 1;
+
+   return 0;
+}
+
+