From 3485fc41bcb8b082815b7d5e48a080c1fcfbab38 Mon Sep 17 00:00:00 2001
From: Mark Wooding <mdw@distorted.org.uk>
Date: Tue, 4 Apr 2006 17:20:05 +0100
Subject: [PATCH] mpint: Fix misbehaviour on larger-than-mpw integer types.

The old implementation of MP_FROMINT was grievously broken, it turns
out.  Handle positive and negative numbers separately.
---
 mpint.h     | 57 ++++++++++++++++++++++++---------------------------------
 tests/mpint | 12 ++++++++++++
 2 files changed, 36 insertions(+), 33 deletions(-)

diff --git a/mpint.h b/mpint.h
index 23378cd..e44c39e 100644
--- a/mpint.h
+++ b/mpint.h
@@ -63,42 +63,33 @@
   MP_DEST(_d, _sz, 0);							\
   _d->f &= ~(MP_NEG | MP_UNDEF);					\
 									\
-  /* --- Set the sign on the MP --- *					\
-   *									\
-   * If the input integer is *not* negative, then negate it.  This	\
-   * fixes a problem with two's complement machines where the most	\
-   * negative value actually has larger magnitude than the most		\
-   * positive, and hence -TYPE_MIN == TYPE_MIN but TYPE_MIN != 0.  If	\
-   * all the work is carried out on negative numbers there isn't a	\
-   * problem.								\
-   */									\
-									\
-  if (_i >= 0)								\
-    _i = -_i;								\
-  else									\
+  if (_i >= 0) {							\
+    while (_i) {							\
+      if (_o == _sz) {							\
+	_sz <<= 1;							\
+	MP_ENSURE(_d, _sz);						\
+      }									\
+      _d->v[_o++] = MPW(_i);						\
+      if (_i < MPW_MAX)							\
+	break;								\
+      else								\
+	_i /= (type)MPW_MAX + 1;					\
+    }									\
+  } else {								\
     _d->f |= MP_NEG;							\
-									\
-  while (_i) {								\
-    if (_o == _sz) {							\
-      _sz <<= 1;							\
-      MP_ENSURE(_d, _sz);						\
+    while (_i) {							\
+      if (_o == _sz) {							\
+	_sz <<= 1;							\
+	MP_ENSURE(_d, _sz);						\
+      }									\
+      _d->v[_o++] = MPW(-_i);						\
+      if (_i > -MPW_MAX)						\
+	break;								\
+      else								\
+	_i /= (type)MPW_MAX + 1;					\
     }									\
-    _d->v[_o++] = MPW(-_i);						\
-									\
-    /* --- More subtlety --- *						\
-     *									\
-     * Ideally, I'd like to just shift @i@ right by @MPW_BITS@.  But I	\
-     * can't, because that might be more than I'm allowed.  I can't	\
-     * divide by @MPW_MAX + 1@ because that might turn out to be zero	\
-     * in my current type, and besides which it's unsigned which messes	\
-     * up all of my negative arithmetic.  So do an explicit test here.	\
-     */									\
-									\
-    if (_i >= -MPW_MAX)							\
-      break;								\
-    else								\
-      _i /= (type)MPW_MAX + 1;						\
   }									\
+									\
   _d->vl = _d->v + _o;							\
   (d) = _d;								\
 } while (0)
diff --git a/tests/mpint b/tests/mpint
index c4faa39..49157ba 100644
--- a/tests/mpint
+++ b/tests/mpint
@@ -9,6 +9,9 @@ fromuint {
   0 0;
   1 1;
   -5 0xfffffffb;
+  0x7ffff 0x7ffff;
+  0x80000 0x80000;
+  0xfffff 0xfffff;
   0x7fffffff 0x7fffffff;
   0x80000000 0x80000000;		# Bastard torture test
   0xffffffff 0xffffffff;
@@ -18,6 +21,9 @@ fromint {
   0 0;
   1 1;
   -5 -5;
+  0x7ffff 0x7ffff;
+  0x80000 0x80000;
+  0xfffff 0xfffff;
   0x7fffffff 0x7fffffff;
   -0x80000000 -0x80000000;		# Bastard torture test
 }
@@ -26,6 +32,9 @@ touint {
   0 0;
   1 1;
   -5 -5;
+  0x7ffff 0x7ffff;
+  0x80000 0x80000;
+  0xfffff 0xfffff;
   0x7fffffff 0x7fffffff;
   0x80000000 -0x80000000;		# Bastard torture test
   0xffffffff 0xffffffff;
@@ -35,6 +44,9 @@ toint {
   0 0;
   1 1;
   -5 -5;
+  0x7ffff 0x7ffff;
+  0x80000 0x80000;
+  0xfffff 0xfffff;
   0x7fffffff 0x7fffffff;
   -0x80000000 -0x80000000;		# Bastard torture test
 }
-- 
2.11.0