rtexif: Fix conversion from RATIONAL to int, double or string

RATIONAL tags are defined as a ratio of two LONG, themselves defined as
32-bit unsigned integers. The value is misinterpreted when converting to
an int, double or string, as the numerator and the denominator are
interpreted as signed values. The problem has been noticed with the
ExposureTime tag generated by libtiff, which sets the denominator to
0xffffffff for exposure times lower than 1. Fix it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

rtexif/rtexif.cc

@@ -1510,8 +1510,6 @@ int Tag::toInt (int ofs, TagType astype) const
         return attrib->interpreter->toInt (this, ofs, astype);
     }
 
-    int a;
-
     if (astype == INVALID) {
         astype = type;
     }
@@ -1537,10 +1535,15 @@ int Tag::toInt (int ofs, TagType astype) const
         case LONG:
             return (int)sget4 (value + ofs, getOrder());
 
-        case SRATIONAL:
+        case SRATIONAL: {
-        case RATIONAL:
+            int a = (int)sget4 (value + ofs + 4, getOrder());
-            a = (int)sget4 (value + ofs + 4, getOrder());
             return a == 0 ? 0 : (int)sget4 (value + ofs, getOrder()) / a;
+        }
+
+        case RATIONAL: {
+            uint32_t a = (uint32_t)sget4 (value + ofs + 4, getOrder());
+            return a == 0 ? 0 : (uint32_t)sget4 (value + ofs, getOrder()) / a;
+        }
 
         case FLOAT:
             return (int)toDouble (ofs);
@@ -1589,10 +1592,14 @@ double Tag::toDouble (int ofs) const
             return (double) ((int)sget4 (value + ofs, getOrder()));
 
         case SRATIONAL:
-        case RATIONAL:
             ud = (int)sget4 (value + ofs, getOrder());
             dd = (int)sget4 (value + ofs + 4, getOrder());
-            return dd == 0. ? 0. : (double)ud / (double)dd;
+            return dd == 0. ? 0. : ud / dd;
+
+        case RATIONAL:
+            ud = (uint32_t)sget4 (value + ofs, getOrder());
+            dd = (uint32_t)sget4 (value + ofs + 4, getOrder());
+            return dd == 0. ? 0. : ud / dd;
 
         case FLOAT:
             conv.i = sget4 (value + ofs, getOrder());
@@ -1735,10 +1742,13 @@ void Tag::toString (char* buffer, int ofs) const
                 break;
 
             case SRATIONAL:
-            case RATIONAL:
                 sprintf (b, "%d/%d", (int)sget4 (value + 8 * i + ofs, getOrder()), (int)sget4 (value + 8 * i + ofs + 4, getOrder()));
                 break;
 
+            case RATIONAL:
+                sprintf (b, "%u/%u", (uint32_t)sget4 (value + 8 * i + ofs, getOrder()), (uint32_t)sget4 (value + 8 * i + ofs + 4, getOrder()));
+                break;
+
             case FLOAT:
                 sprintf (b, "%g", toDouble (8 * i + ofs));
                 break;

rtexif/rtexif.h

@@ -434,13 +434,18 @@ public:
             case LONG:
                 return (double) ((int)sget4 (t->getValue() + ofs, t->getOrder()));
 
-            case SRATIONAL:
+            case SRATIONAL: {
-            case RATIONAL: {
                 const double dividend = (int)sget4 (t->getValue() + ofs, t->getOrder());
                 const double divisor = (int)sget4 (t->getValue() + ofs + 4, t->getOrder());
                 return divisor == 0. ? 0. : dividend / divisor;
             }
 
+            case RATIONAL: {
+                const double dividend = (uint32_t)sget4 (t->getValue() + ofs, t->getOrder());
+                const double divisor = (uint32_t)sget4 (t->getValue() + ofs + 4, t->getOrder());
+                return divisor == 0. ? 0. : dividend / divisor;
+            }
+
             case FLOAT:
                 return double (sget4 (t->getValue() + ofs, t->getOrder()));
 
@@ -454,8 +459,6 @@ public:
     // Get the value as an int
     virtual int toInt (const Tag* t, int ofs = 0, TagType astype = INVALID)
     {
-        int a;
-
         if (astype == INVALID || astype == AUTO) {
             astype = t->getType();
         }
@@ -480,10 +483,15 @@ public:
             case LONG:
                 return (int)sget4 (t->getValue() + ofs, t->getOrder());
 
-            case SRATIONAL:
+            case SRATIONAL: {
-            case RATIONAL:
+                int a = (int)sget4 (t->getValue() + ofs + 4, t->getOrder());
-                a = (int)sget4 (t->getValue() + ofs + 4, t->getOrder());
                 return a == 0 ? 0 : (int)sget4 (t->getValue() + ofs, t->getOrder()) / a;
+            }
+
+            case RATIONAL: {
+                uint32_t a = (uint32_t)sget4 (t->getValue() + ofs + 4, t->getOrder());
+                return a == 0 ? 0 : (uint32_t)sget4 (t->getValue() + ofs, t->getOrder()) / a;
+            }
 
             case FLOAT:
                 return (int)toDouble (t, ofs);