Parse large floats as infinity (#1349) (#1353)

Return 1.9.1 functionality where values too large to fit in
double are converted to positive or negative infinity.

Commit 645cd04 changed functionality so that large floats cause
parse error, while version 1.9.1 accepted them as infinite.
This is problematic because writer outputs infinity values
as `1e+9999`, which could no longer be parsed back.

Fixed also legacy Reader even though it did not parse large values
even before breaking change, due to problematic output/parse asymmetry.

`>>` operator sets value to numeric_limits::max/lowest value if
representation is too large to fit to double. [1][2] In macos
value appears to be parsed to infinity.

> | value in *val*           | description |
> |--------------------------|-------------|
> | numeric_limits::max()    | The sequence represents a value too large for the type of val |
> | numeric_limits::lowest() | The sequence represents a value too large negative for the type of val |

[1] https://www.cplusplus.com/reference/istream/istream/operator%3E%3E/
[2] https://www.cplusplus.com/reference/locale/num_get/get/

Signed-off-by: Tero Kinnunen <tero.kinnunen@vaisala.com>

Co-authored-by: Tero Kinnunen <tero.kinnunen@vaisala.com>

src/lib_json/json_reader.cpp

@@ -12,6 +12,7 @@
 #endif // if !defined(JSON_IS_AMALGAMATION)
 #include <algorithm>
 #include <cassert>
+#include <cmath>
 #include <cstring>
 #include <iostream>
 #include <istream>
@@ -600,9 +601,15 @@ bool Reader::decodeDouble(Token& token, Value& decoded) {
   double value = 0;
   String buffer(token.start_, token.end_);
   IStringStream is(buffer);
-  if (!(is >> value))
-    return addError(
+  if (!(is >> value)) {
+    if (value == std::numeric_limits<double>::max())
+      value = std::numeric_limits<double>::infinity();
+    else if (value == std::numeric_limits<double>::lowest())
+      value = -std::numeric_limits<double>::infinity();
+    else if (!std::isinf(value))
+      return addError(
         "'" + String(token.start_, token.end_) + "' is not a number.", token);
+  }
   decoded = value;
   return true;
 }
@@ -1647,7 +1654,12 @@ bool OurReader::decodeDouble(Token& token, Value& decoded) {
   const String buffer(token.start_, token.end_);
   IStringStream is(buffer);
   if (!(is >> value)) {
-    return addError(
+    if (value == std::numeric_limits<double>::max())
+      value = std::numeric_limits<double>::infinity();
+    else if (value == std::numeric_limits<double>::lowest())
+      value = -std::numeric_limits<double>::infinity();
+    else if (!std::isinf(value))
+      return addError(
         "'" + String(token.start_, token.end_) + "' is not a number.", token);
   }
   decoded = value;

test/data/legacy_test_real_13.expected

@@ -0,0 +1,3 @@
+.=[]
+.[0]=-inf
+.[1]=inf

test/data/legacy_test_real_13.json

@@ -0,0 +1 @@
+[-1e+9999, 1e+9999]