Fix issue #380: Signed integer overflow check

Instead of checking something like `x * y + z > max` where `x * y` can overflow, check for `x > (max - z) / y` instead.

Fix issue #380: Signed integer overflow check
1e981115 · Yixin Zhang · 79fa8b2f · 1e981115 · 1e981115
Commit 1e981115 authored Dec 09, 2016 by Yixin Zhang
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Showing with 6 additions and 6 deletions

json.hpp src/json.hpp +0 -0

json.hpp.re2c src/json.hpp.re2c +6 -6

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--- a/src/json.hpp
+++ b/src/json.hpp
--- a/src/json.hpp.re2c
+++ b/src/json.hpp.re2c
@@ -9769,19 +9769,19 @@ class basic_json
                // skip if definitely not an integer
                if (type != value_t::number_float)
                {
-                    // multiply last value by ten and add the new digit
+                    auto digit = *curptr - '0';
-                    auto temp = value * 10 + *curptr - '0';
-                    // test for overflow
+                    // overflow if value * 10 + digit > max, move terms around
-                    if (temp < value || temp > max)
+                    // to avoid overflow in intermediate values
+                    if (value > (max - digit) / 10)
                    {
                        // overflow
                        type = value_t::number_float;
                    }
                    else
                    {
-                        // no overflow - save it
+                        // no overflow
-                        value = temp;
+                        value = value * 10 + digit;
                    }
                }
            }