Fixed a bug in the bigint object that caused division to sometimes produce

incorrect results.

dlib/bigint/bigint_kernel_1.cpp

@@ -1284,17 +1284,13 @@ namespace dlib
             ++r;
         }
 
-        // if we are using one less digit
-        if (*(r-1) == 0)
-        {
-            if (lhs->digits_used != 1)
-                result->digits_used = lhs->digits_used - 1;
-            else
-                result->digits_used = 1;
-        }
-        else
-        {
         result->digits_used = lhs->digits_used;
+        // adjust the number of digits used appropriately 
+        --r;
+        while (*r == 0 && result->digits_used > 1)
+        {
+            --r;
+            --result->digits_used;
         }
     }
 
@@ -1344,7 +1340,7 @@ namespace dlib
         // shift rhs left until it is one shift away from being larger than lhs and
         // put the number of left shifts necessary into shifts
         uint32 shifts; 
-        shifts = (lhs->digits_used - rhs->digits_used) * 8;
+        shifts = (lhs->digits_used - rhs->digits_used) * 16;
 
         shift_left(rhs,&temp,shifts);
 

dlib/bigint/bigint_kernel_2.cpp

@@ -1285,17 +1285,13 @@ namespace dlib
             ++r;
         }
 
-        // if we are using one less digit
-        if (*(r-1) == 0)
-        {
-            if (lhs->digits_used != 1)
-                result->digits_used = lhs->digits_used - 1;
-            else
-                result->digits_used = 1;
-        }
-        else
-        {
         result->digits_used = lhs->digits_used;
+        // adjust the number of digits used appropriately 
+        --r;
+        while (*r == 0 && result->digits_used > 1)
+        {
+            --r;
+            --result->digits_used;
         }
     }
 
@@ -1345,7 +1341,7 @@ namespace dlib
         // shift rhs left until it is one shift away from being larger than lhs and
         // put the number of left shifts necessary into shifts
         uint32 shifts; 
-        shifts = (lhs->digits_used - rhs->digits_used) * 8;
+        shifts = (lhs->digits_used - rhs->digits_used) * 16;
 
         shift_left(rhs,&temp,shifts);
 
@@ -1523,7 +1519,7 @@ namespace dlib
             // that should happen.
             ifft(a,size);
 
-            // loop over the result and propigate any carries that need to take place.  
+            // loop over the result and propagate any carries that need to take place.  
             // We will also be moving the resulting numbers into result->number at 
             // the same time.
             uint64 carry = 0;

dlib/test/bigint.cpp

@@ -473,6 +473,15 @@ namespace
 
 
 
+        a = 10000;
+        a = a*a*a*a; a = a*a; a = a*a;
+        b = 2;
+        DLIB_TEST((a/b)*b == a);
+
+        a = 10000*5;
+        a = a*a*a*a; a = a*a; a = a*a;
+        b = 5;
+        DLIB_TEST((a/b)*b == a);
     }