Remove component size limit for version comparisons

The VersionCompare() function converted version components to
'unsigned long' prior to comparing them.  Any version components
too large for 'unsigned long' were treated as equal to ULONG_MAX.
This impacted operators like VERSION_GREATER, VERSION_LESS, and
VERSION_EQUAL.  The new code does not limit the length of the
version components for valid comparisons.

Source/cmSystemTools.cxx

@@ -3197,20 +3197,41 @@ bool VersionCompare(cmSystemTools::CompareOp op, const char* lhss,
 {
   const char* endl = lhss;
   const char* endr = rhss;
-  unsigned long lhs;
-  unsigned long rhs;
 
   while (((*endl >= '0') && (*endl <= '9')) ||
          ((*endr >= '0') && (*endr <= '9'))) {
-    // Do component-wise comparison.
-    lhs = strtoul(endl, const_cast<char**>(&endl), 10);
-    rhs = strtoul(endr, const_cast<char**>(&endr), 10);
+    // Do component-wise comparison, ignoring leading zeros
+    // (components are treated as integers, not as mantissas)
+    while (*endl == '0') {
+      endl++;
+    }
+    while (*endr == '0') {
+      endr++;
+    }
+
+    const char* beginl = endl;
+    const char* beginr = endr;
+
+    // count significant digits
+    while ((*endl >= '0') && (*endl <= '9')) {
+      endl++;
+    }
+    while ((*endr >= '0') && (*endr <= '9')) {
+      endr++;
+    }
+
+    // compare number of digits first
+    ptrdiff_t r = ((endl - beginl) - (endr - beginr));
+    if (r == 0) {
+      // compare the digits if number of digits is equal
+      r = strncmp(beginl, beginr, endl - beginl);
+    }
 
-    if (lhs < rhs) {
+    if (r < 0) {
       // lhs < rhs, so true if operation is LESS
       return (op & cmSystemTools::OP_LESS) != 0;
     }
-    if (lhs > rhs) {
+    if (r > 0) {
       // lhs > rhs, so true if operation is GREATER
       return (op & cmSystemTools::OP_GREATER) != 0;
     }

Tests/CMakeLib/testSystemTools.cxx

@@ -61,8 +61,26 @@ int testSystemTools(int /*unused*/, char* /*unused*/[])
            "VersionCompareEqual different length");
   cmAssert(cmSystemTools::VersionCompareGreater("6.2.1", "6.2"),
            "VersionCompareGreater different length");
-  cmAssert(cmSystemTools::VersionCompareGreater("3.141592653", "3.14159265"),
-           "VersionCompareGreater more digits");
+  cmAssert(
+    !cmSystemTools::VersionCompareEqual(
+      "3.14159265358979323846264338327950288419716939937510582097494459230",
+      "3.14159265358979323846264338327950288419716939937510582097494459231"),
+    "VersionCompareEqual long number");
+  cmAssert(
+    !cmSystemTools::VersionCompareGreater(
+      "3.14159265358979323846264338327950288419716939937510582097494459230",
+      "3.14159265358979323846264338327950288419716939937510582097494459231"),
+    "VersionCompareGreater long number");
+  cmAssert(
+    !cmSystemTools::VersionCompareEqual(
+      "3.141592653589793238462643383279502884197169399375105820974944592307",
+      "3.14159265358979323846264338327950288419716939937510582097494459231"),
+    "VersionCompareEqual more digits");
+  cmAssert(
+    cmSystemTools::VersionCompareGreater(
+      "3.141592653589793238462643383279502884197169399375105820974944592307",
+      "3.14159265358979323846264338327950288419716939937510582097494459231"),
+    "VersionCompareGreater more digits");
 
   // ----------------------------------------------------------------------
   // Test cmSystemTools::strverscmp