Add Writer::SetMaxDecimalPlaces()

include/rapidjson/internal/dtoa.h

@@ -145,7 +145,7 @@ inline char* WriteExponent(int K, char* buffer) {
     return buffer;
 }
 
-inline char* Prettify(char* buffer, int length, int k) {
+inline char* Prettify(char* buffer, int length, int k, int maxDecimalPlaces) {
     const int kk = length + k;  // 10^(kk-1) <= v < 10^kk
 
     if (length <= kk && kk <= 21) {
@@ -160,7 +160,16 @@ inline char* Prettify(char* buffer, int length, int k) {
         // 1234e-2 -> 12.34
         std::memmove(&buffer[kk + 1], &buffer[kk], static_cast<size_t>(length - kk));
         buffer[kk] = '.';
-        return &buffer[length + 1];
+        if (length > kk + maxDecimalPlaces) {
+            // When maxDecimalPlaces = 2, 1.2345 -> 1.23, 1.102 -> 1.1
+            // Remove extra trailing zeros (at least one) after truncation.
+            for (int i = kk + maxDecimalPlaces; i > kk + 1; i--)
+                if (buffer[i] != '0')
+                    return &buffer[i + 1];
+            return &buffer[kk + 2]; // Reserve one zero
+        }
+        else
+            return &buffer[length + 1];
     }
     else if (-6 < kk && kk <= 0) {
         // 1234e-6 -> 0.001234
@@ -170,7 +179,23 @@ inline char* Prettify(char* buffer, int length, int k) {
         buffer[1] = '.';
         for (int i = 2; i < offset; i++)
             buffer[i] = '0';
-        return &buffer[length + offset];
+        if (length + offset > maxDecimalPlaces) {
+            // When maxDecimalPlaces = 2, 0.123 -> 0.12, 0.102 -> 0.1
+            // Remove extra trailing zeros (at least one) after truncation.
+            for (int i = maxDecimalPlaces + 1; i > 2; i--)
+                if (buffer[i] != '0')
+                    return &buffer[i + 1];
+            return &buffer[3]; // Reserve one zero
+        }
+        else
+            return &buffer[length + offset];
+    }
+    else if (kk < -maxDecimalPlaces) {
+        // Truncate to zero
+        buffer[0] = '0';
+        buffer[1] = '.';
+        buffer[2] = '0';
+        return &buffer[3];
     }
     else if (length == 1) {
         // 1e30
@@ -186,7 +211,8 @@ inline char* Prettify(char* buffer, int length, int k) {
     }
 }
 
-inline char* dtoa(double value, char* buffer) {
+inline char* dtoa(double value, char* buffer, int maxDecimalPlaces = 324) {
+    RAPIDJSON_ASSERT(maxDecimalPlaces >= 1);
     Double d(value);
     if (d.IsZero()) {
         if (d.Sign())
@@ -203,7 +229,7 @@ inline char* dtoa(double value, char* buffer) {
         }
         int length, K;
         Grisu2(value, buffer, &length, &K);
-        return Prettify(buffer, length, K);
+        return Prettify(buffer, length, K, maxDecimalPlaces);
     }
 }
 

include/rapidjson/writer.h

@@ -56,6 +56,8 @@ class Writer {
 public:
     typedef typename SourceEncoding::Ch Ch;
 
+    static const int kDefaultMaxDecimalPlaces = 324;
+
     //! Constructor
     /*! \param os Output stream.
         \param stackAllocator User supplied allocator. If it is null, it will create a private one.
@@ -63,11 +65,11 @@ public:
     */
     explicit
     Writer(OutputStream& os, StackAllocator* stackAllocator = 0, size_t levelDepth = kDefaultLevelDepth) : 
-        os_(&os), level_stack_(stackAllocator, levelDepth * sizeof(Level)), hasRoot_(false) {}
+        os_(&os), level_stack_(stackAllocator, levelDepth * sizeof(Level)), maxDecimalPlaces_(kDefaultMaxDecimalPlaces), hasRoot_(false) {}
 
     explicit
     Writer(StackAllocator* allocator = 0, size_t levelDepth = kDefaultLevelDepth) :
-        os_(0), level_stack_(allocator, levelDepth * sizeof(Level)), hasRoot_(false) {}
+        os_(0), level_stack_(allocator, levelDepth * sizeof(Level)), maxDecimalPlaces_(kDefaultMaxDecimalPlaces), hasRoot_(false) {}
 
     //! Reset the writer with a new stream.
     /*!
@@ -101,6 +103,35 @@ public:
         return hasRoot_ && level_stack_.Empty();
     }
 
+    int GetMaxDecimalPlaces() const {
+        return maxDecimalPlaces_;
+    }
+
+    //! Sets the maximum number of decimal places for double output.
+    /*!
+        This setting truncates the output with specified number of decimal places.
+
+        For example, 
+
+        \code
+        writer.SetMaxDecimalPlaces(3);
+        writer.StartArray();
+        writer.Double(0.12345);                 // "0.123"
+        writer.Double(0.0001);                  // "0.0"
+        writer.Double(1.234567890123456e30);    // "1.234567890123456e30" (do not truncate significand for positive exponent)
+        writer.Double(1.23e-4);                 // "0.0"                  (do truncate significand for negative exponent)
+        writer.EndArray();
+        \endcode
+
+        The default setting does not truncate any decimal places. You can restore to this setting by calling
+        \code
+        writer.SetMaxDecimalPlaces(Writer::kDefaultMaxDecimalPlaces);
+        \endcode
+    */
+    void SetMaxDecimalPlaces(int maxDecimalPlaces) {
+        maxDecimalPlaces_ = maxDecimalPlaces;
+    }
+
     /*!@name Implementation of Handler
         \see Handler
     */
@@ -246,7 +277,7 @@ protected:
             return false;
         
         char buffer[25];
-        char* end = internal::dtoa(d, buffer);
+        char* end = internal::dtoa(d, buffer, maxDecimalPlaces_);
         PutReserve(*os_, static_cast<size_t>(end - buffer));
         for (char* p = buffer; p != end; ++p)
             PutUnsafe(*os_, static_cast<typename TargetEncoding::Ch>(*p));
@@ -353,6 +384,7 @@ protected:
 
     OutputStream* os_;
     internal::Stack<StackAllocator> level_stack_;
+    int maxDecimalPlaces_;
     bool hasRoot_;
 
 private:
@@ -401,7 +433,7 @@ inline bool Writer<StringBuffer>::WriteDouble(double d) {
         return false;
     
     char *buffer = os_->Push(25);
-    char* end = internal::dtoa(d, buffer);
+    char* end = internal::dtoa(d, buffer, maxDecimalPlaces_);
     os_->Pop(static_cast<size_t>(25 - (end - buffer)));
     return true;
 }

test/unittest/CMakeLists.txt

@@ -2,6 +2,7 @@ set(UNITTEST_SOURCES
 	allocatorstest.cpp
     bigintegertest.cpp
     documenttest.cpp
+    dtoatest.cpp
     encodedstreamtest.cpp
     encodingstest.cpp
     fwdtest.cpp

test/unittest/dtoatest.cpp

+// Tencent is pleased to support the open source community by making RapidJSON available.
+// 
+// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
+//
+// Licensed under the MIT License (the "License"); you may not use this file except
+// in compliance with the License. You may obtain a copy of the License at
+//
+// http://opensource.org/licenses/MIT
+//
+// Unless required by applicable law or agreed to in writing, software distributed 
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the 
+// specific language governing permissions and limitations under the License.
+
+#include "unittest.h"
+#include "rapidjson/internal/dtoa.h"
+
+#ifdef __GNUC__
+RAPIDJSON_DIAG_PUSH
+RAPIDJSON_DIAG_OFF(type-limits)
+#endif
+
+using namespace rapidjson::internal;
+
+TEST(dtoa, normal) {
+    char buffer[30];
+
+#define TEST_DTOA(d, a)\
+    *dtoa(d, buffer) = '\0';\
+    EXPECT_STREQ(a, buffer)
+
+    TEST_DTOA(0.0, "0.0");
+    TEST_DTOA(-0.0, "-0.0");
+    TEST_DTOA(1.0, "1.0");
+    TEST_DTOA(-1.0, "-1.0");
+    TEST_DTOA(1.2345, "1.2345");
+    TEST_DTOA(1.2345678, "1.2345678");
+    TEST_DTOA(0.123456789012, "0.123456789012");
+    TEST_DTOA(1234567.8, "1234567.8");
+    TEST_DTOA(0.000001, "0.000001");
+    TEST_DTOA(0.0000001, "1e-7");
+    TEST_DTOA(1e30, "1e30");
+    TEST_DTOA(1.234567890123456e30, "1.234567890123456e30");
+    TEST_DTOA(5e-324, "5e-324"); // Min subnormal positive double
+    TEST_DTOA(2.225073858507201e-308, "2.225073858507201e-308"); // Max subnormal positive double
+    TEST_DTOA(2.2250738585072014e-308, "2.2250738585072014e-308"); // Min normal positive double
+    TEST_DTOA(1.7976931348623157e308, "1.7976931348623157e308"); // Max double
+
+#undef TEST_DTOA
+}
+
+TEST(dtoa, maxDecimalPlaces) {
+    char buffer[30];
+
+#define TEST_DTOA(m, d, a)\
+    *dtoa(d, buffer, m) = '\0';\
+    EXPECT_STREQ(a, buffer)
+
+    TEST_DTOA(3, 0.0, "0.0");
+    TEST_DTOA(1, 0.0, "0.0");
+    TEST_DTOA(3, -0.0, "-0.0");
+    TEST_DTOA(3, 1.0, "1.0");
+    TEST_DTOA(3, -1.0, "-1.0");
+    TEST_DTOA(3, 1.2345, "1.234");
+    TEST_DTOA(2, 1.2345, "1.23");
+    TEST_DTOA(1, 1.2345, "1.2");
+    TEST_DTOA(3, 1.2345678, "1.234");
+    TEST_DTOA(3, 1.0001, "1.0");
+    TEST_DTOA(2, 1.0001, "1.0");
+    TEST_DTOA(1, 1.0001, "1.0");
+    TEST_DTOA(3, 0.123456789012, "0.123");
+    TEST_DTOA(2, 0.123456789012, "0.12");
+    TEST_DTOA(1, 0.123456789012, "0.1");
+    TEST_DTOA(4, 0.0001, "0.0001");
+    TEST_DTOA(3, 0.0001, "0.0");
+    TEST_DTOA(2, 0.0001, "0.0");
+    TEST_DTOA(1, 0.0001, "0.0");
+    TEST_DTOA(3, 1234567.8, "1234567.8");
+    TEST_DTOA(3, 1e30, "1e30");
+    TEST_DTOA(3, 5e-324, "0.0"); // Min subnormal positive double
+    TEST_DTOA(3, 2.225073858507201e-308, "0.0"); // Max subnormal positive double
+    TEST_DTOA(3, 2.2250738585072014e-308, "0.0"); // Min normal positive double
+    TEST_DTOA(3, 1.7976931348623157e308, "1.7976931348623157e308"); // Max double
+
+#undef TEST_DTOA
+}
+
+
+#ifdef __GNUC__
+RAPIDJSON_DIAG_POP
+#endif