QUtil::double_to_string: trim trailing zeroes with option to disable

ChangeLog

@@ -1,3 +1,15 @@
+2021-02-12  Jay Berkenbilt  <[email protected]>
+
+	* QUtil::double_to_string: trim trailing zeroes by default, and
+	add option to not trim trailing zeroes. This causes a syntactic
+	but semantically preserving change in output when doubles are
+	converted to strings. The library uses double_to_string in only a
+	few places. In practice, output will be different (trailing zeroes
+	removed) in code that creates form XObjects (mostly generation of
+	appearance streams for form fields as well as overlay and
+	underlay) and in the flatten rotation code that was added in qpdf
+	10.1.
+
 2021-02-10  Jay Berkenbilt  <[email protected]>
 
 	* Require a C++-14 compiler.

include/qpdf/QPDFObjectHandle.hh

@@ -476,6 +476,11 @@ class QPDFObjectHandle
     static QPDFObjectHandle newReal(std::string const& value);
     QPDF_DLL
     static QPDFObjectHandle newReal(double value, int decimal_places = 0);
+    // ABI: combine with other newReal by adding trim_trailing_zeroes
+    // above as an optional parameter with a default of true.
+    QPDF_DLL
+    static QPDFObjectHandle newReal(double value, int decimal_places,
+                                    bool trim_trailing_zeroes);
     QPDF_DLL
     static QPDFObjectHandle newName(std::string const& name);
     QPDF_DLL

include/qpdf/QUtil.hh

@@ -47,9 +47,16 @@ namespace QUtil
     QPDF_DLL
     std::string int_to_string_base(long long, int base, int length = 0);
     QPDF_DLL
-    std::string uint_to_string_base(unsigned long long, int base, int length = 0);
+    std::string uint_to_string_base(unsigned long long, int base,
+                                    int length = 0);
     QPDF_DLL
     std::string double_to_string(double, int decimal_places = 0);
+    // ABI: combine with other double_to_string by adding
+    // trim_trailing_zeroes above as an optional parameter with a
+    // default of true.
+    QPDF_DLL
+    std::string double_to_string(double, int decimal_places,
+                                 bool trim_trailing_zeroes);
 
     // These string to number methods throw std::runtime_error on
     // underflow/overflow.

libqpdf/QPDFObjectHandle.cc

@@ -2422,7 +2422,16 @@ QPDFObjectHandle::newReal(std::string const& value)
 QPDFObjectHandle
 QPDFObjectHandle::newReal(double value, int decimal_places)
 {
-    return QPDFObjectHandle(new QPDF_Real(value, decimal_places));
+    return QPDFObjectHandle(
+        new QPDF_Real(value, decimal_places, true));
+}
+
+QPDFObjectHandle
+QPDFObjectHandle::newReal(double value, int decimal_places,
+                          bool trim_trailing_zeroes)
+{
+    return QPDFObjectHandle(
+        new QPDF_Real(value, decimal_places, trim_trailing_zeroes));
 }
 
 QPDFObjectHandle

libqpdf/QPDF_Real.cc

@@ -7,8 +7,9 @@ QPDF_Real::QPDF_Real(std::string const& val) :
 {
 }
 
-QPDF_Real::QPDF_Real(double value, int decimal_places) :
-    val(QUtil::double_to_string(value, decimal_places))
+QPDF_Real::QPDF_Real(double value, int decimal_places,
+                     bool trim_trailing_zeroes) :
+    val(QUtil::double_to_string(value, decimal_places, trim_trailing_zeroes))
 {
 }
 

libqpdf/QUtil.cc

@@ -323,19 +323,38 @@ QUtil::uint_to_string_base(unsigned long long num, int base, int length)
 
 std::string
 QUtil::double_to_string(double num, int decimal_places)
+{
+    return double_to_string(num, decimal_places, true);
+}
+
+std::string
+QUtil::double_to_string(double num, int decimal_places,
+                        bool trim_trailing_zeroes)
 {
     // Backward compatibility -- this code used to use sprintf and
     // treated decimal_places <= 0 to mean to use the default, which
-    // was six decimal places.  Also sprintf with %*.f interprets the
-    // length as fixed point rather than significant figures.
+    // was six decimal places. Starting in 10.2, we trim trailing
+    // zeroes by default.
     if (decimal_places <= 0)
     {
         decimal_places = 6;
     }
     std::ostringstream buf;
     buf.imbue(std::locale::classic());
     buf << std::setprecision(decimal_places) << std::fixed << num;
-    return buf.str();
+    std::string result = buf.str();
+    if (trim_trailing_zeroes)
+    {
+        while ((result.length() > 1) && (result.back() == '0'))
+        {
+            result.pop_back();
+        }
+        if ((result.length() > 1) && (result.back() == '.'))
+        {
+            result.pop_back();
+        }
+    }
+    return result;
 }
 
 long long

libqpdf/qpdf/QPDF_Real.hh

@@ -7,7 +7,7 @@ class QPDF_Real: public QPDFObject
 {
   public:
     QPDF_Real(std::string const& val);
-    QPDF_Real(double value, int decimal_places = 0);
+    QPDF_Real(double value, int decimal_places, bool trim_trailing_zeroes);
     virtual ~QPDF_Real();
     virtual std::string unparse();
     virtual JSON getJSON();

libtests/json.cc

@@ -36,7 +36,7 @@ static void test_main()
           "  \"a\\tb\",\n"
           "  null,\n"
           "  16059,\n"
-          "  3.141590,\n"
+          "  3.14159,\n"
           "  2.1e5\n"
           "]");
     JSON jmap = JSON::makeDictionary();
@@ -56,7 +56,7 @@ static void test_main()
           "    \"a\\tb\",\n"
           "    null,\n"
           "    16059,\n"
-          "    3.141590,\n"
+          "    3.14159,\n"
           "    2.1e5\n"
           "  ],\n"
           "  \"b\": \"a\\tb\",\n"

libtests/matrix.cc

@@ -44,39 +44,39 @@ static void check_rect(QPDFObjectHandle::Rectangle const& r,
 int main()
 {
     QPDFMatrix m;
-    check(m, "1.00000 0.00000 0.00000 1.00000 0.00000 0.00000");
+    check(m, "1 0 0 1 0 0");
     m.translate(10, 20);
-    check(m, "1.00000 0.00000 0.00000 1.00000 10.00000 20.00000");
+    check(m, "1 0 0 1 10 20");
     m.scale(1.5, 2);
-    check(m, "1.50000 0.00000 0.00000 2.00000 10.00000 20.00000");
+    check(m, "1.5 0 0 2 10 20");
     double xp = 0;
     double yp = 0;
     m.transform(10, 100, xp, yp);
-    check_xy(xp, yp, "25.00 220.00");
+    check_xy(xp, yp, "25 220");
     m.translate(30, 40);
-    check(m, "1.50000 0.00000 0.00000 2.00000 55.00000 100.00000");
+    check(m, "1.5 0 0 2 55 100");
     m.transform(10, 100, xp, yp);
-    check_xy(xp, yp, "70.00 300.00");
+    check_xy(xp, yp, "70 300");
     m.concat(QPDFMatrix(1, 2, 3, 4, 5, 6));
-    check(m, "1.50000 4.00000 4.50000 8.00000 62.50000 112.00000");
+    check(m, "1.5 4 4.5 8 62.5 112");
     m.rotatex90(90);
-    check(m, "4.50000 8.00000 -1.50000 -4.00000 62.50000 112.00000");
+    check(m, "4.5 8 -1.5 -4 62.5 112");
     m.rotatex90(180);
-    check(m, "-4.50000 -8.00000 1.50000 4.00000 62.50000 112.00000");
+    check(m, "-4.5 -8 1.5 4 62.5 112");
     m.rotatex90(270);
-    check(m, "-1.50000 -4.00000 -4.50000 -8.00000 62.50000 112.00000");
+    check(m, "-1.5 -4 -4.5 -8 62.5 112");
     m.rotatex90(180);
-    check(m, "1.50000 4.00000 4.50000 8.00000 62.50000 112.00000");
+    check(m, "1.5 4 4.5 8 62.5 112");
     m.rotatex90(12345);
-    check(m, "1.50000 4.00000 4.50000 8.00000 62.50000 112.00000");
+    check(m, "1.5 4 4.5 8 62.5 112");
 
     m.transform(240, 480, xp, yp);
-    check_xy(xp, yp, "2582.50 4912.00");
+    check_xy(xp, yp, "2582.5 4912");
 
     check(QPDFMatrix(
               QPDFObjectHandle::parse(
                   "[3 1 4 1 5 9.26535]").getArrayAsMatrix()),
-          "3.00000 1.00000 4.00000 1.00000 5.00000 9.26535");
+          "3 1 4 1 5 9.26535");
 
     m = QPDFMatrix();
     m.rotatex90(90);

libtests/qtest/qutil/qutil.out

@@ -9,6 +9,12 @@
 0.00012
 0.12346
 0.00012
+1.0102
+1
+1
+1.00000
+10.00
+10
 16059
 37273
 3ebb

libtests/qutil.cc

@@ -117,13 +117,19 @@ void string_conversion_test()
     std::cout << QUtil::int_to_string(16059) << std::endl
 	      << QUtil::int_to_string(16059, 7) << std::endl
 	      << QUtil::int_to_string(16059, -7) << std::endl
-	      << QUtil::double_to_string(3.14159) << std::endl
+	      << QUtil::double_to_string(3.14159, 0, false) << std::endl
 	      << QUtil::double_to_string(3.14159, 3) << std::endl
-	      << QUtil::double_to_string(1000.123, -1024) << std::endl
-              << QUtil::double_to_string(.1234, 5) << std::endl
+	      << QUtil::double_to_string(1000.123, -1024, false) << std::endl
+              << QUtil::double_to_string(.1234, 5, false) << std::endl
               << QUtil::double_to_string(.0001234, 5) << std::endl
               << QUtil::double_to_string(.123456, 5) << std::endl
               << QUtil::double_to_string(.000123456, 5) << std::endl
+              << QUtil::double_to_string(1.01020, 5, true) << std::endl
+              << QUtil::double_to_string(1.00000, 5, true) << std::endl
+              << QUtil::double_to_string(1, 5, true) << std::endl
+              << QUtil::double_to_string(1, 5, false) << std::endl
+              << QUtil::double_to_string(10, 2, false) << std::endl
+              << QUtil::double_to_string(10, 2, true) << std::endl
               << QUtil::int_to_string_base(16059, 10) << std::endl
               << QUtil::int_to_string_base(16059, 8) << std::endl
               << QUtil::int_to_string_base(16059, 16) << std::endl

manual/qpdf-manual.xml

@@ -5068,6 +5068,21 @@ print "\n";
         Library Behavior Changes
        </para>
        <itemizedlist>
+        <listitem>
+         <para>
+          Note: the changes in this section cause differences in
+          output in some cases. These differences change the syntax of
+          the PDF but do not change the semantics (meaning). I make a
+          strong effort to avoid gratuitous changes in qpdf's output
+          so that qpdf changes don't break people's tests. In this
+          case, the changes significantly improve the readability of
+          the generated PDF and don't affect any output that's
+          generated by simple transformation. If you are annoyed by
+          having to update test files, please rest assured that
+          changes like this have been and will continue to be rare
+          events.
+         </para>
+        </listitem>
         <listitem>
          <para>
           <function>QPDFObjectHandle::newUnicodeString</function> now
@@ -5076,7 +5091,19 @@ print "\n";
           reduces needless encoding in UTF-16 of strings that can be
           encoded in ASCII. This change may cause qpdf to generate
           different output than before when form field values are set
-          using <classname>QPDFFormFieldObjectHelper</classname>.
+          using <classname>QPDFFormFieldObjectHelper</classname> but
+          does not change the meaning of the output.
+         </para>
+        </listitem>
+        <listitem>
+         <para>
+          The code that places form XObjects and also the code that
+          flattens rotations trim trailing zeroes from real numbers
+          that they calculate. This causes slight (but semantically
+          equivalent) differences in generated appearance streams and
+          form XObject invocations in overlay/underlay code or in user
+          code that calls the methods that place form XObjects on a
+          page.
          </para>
         </listitem>
        </itemizedlist>
@@ -5184,6 +5211,15 @@ print "\n";
           contents of a file through a pipeline as binary data.
          </para>
         </listitem>
+        <listitem>
+         <para>
+          Add option to <function>QUtil::double_to_string</function>
+          to trim trailing zeroes, which is on by default. Within the
+          qpdf library, this causes changes to output the from code
+          that places form XObjects and the code that flattens
+          rotations.
+         </para>
+        </listitem>
        </itemizedlist>
       </listitem>
       <listitem>

qpdf/qpdf-ctest.c

@@ -634,7 +634,7 @@ static void test24(char const* infile,
         qpdf_oh_new_name(qpdf, "/Quack"));
     qpdf_oh_append_item(
         qpdf, new_array,
-        qpdf_oh_new_real_from_double(qpdf, 4.0, 2));
+        qpdf_oh_new_real_from_double(qpdf, 4.123, 2));
     qpdf_oh_append_item(
         qpdf, new_array,
         qpdf_oh_new_real_from_string(qpdf, "5.0"));

qpdf/test_driver.cc

@@ -560,7 +560,7 @@ void runtest(int n, char const* filename1, char const* arg2)
 	    for (int i = 0; i < nitems; ++i)
 	    {
 		std::cout << QUtil::double_to_string(
-		    qnumbers.getArrayItem(i).getNumericValue(), 3)
+		    qnumbers.getArrayItem(i).getNumericValue(), 3, false)
 			  << std::endl;
 	    }
 	}