json: Fix undefined behaviour when converting integer to double

Coverity doesn't like this, complaining that assignment to an object
with overlapping storage without exact overlap and compatible types can
cause undefined behaviour.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

diff --git a/json/json.c b/json/json.c
index 71a42b8232c7f86e218ead762be7f0a15403d76e..5c961f982baed8bb5de0ba0adc159f8a6445b667 100644 (file)
--- a/json/json.c
+++ b/json/json.c
@@ -783,10 +783,11 @@ json_value * json_parse_ex (json_settings * settings,
                      }
 
                      if (would_overflow(top->u.integer, b))
-                     {  -- num_digits;
+                     {  double dbl = (double)top->u.integer;
+                        -- num_digits;
                         -- state.ptr;
                         top->type = json_double;
-                        top->u.dbl = (double)top->u.integer;
+                        top->u.dbl = dbl;
                         continue;
                      }
 
@@ -816,13 +817,14 @@ json_value * json_parse_ex (json_settings * settings,
                }
                else if (b == '.' && top->type == json_integer)
                {
+                  double dbl = (double)top->u.integer;
                   if (!num_digits)
                   {  sprintf (error, "%d:%d: Expected digit before `.`", line_and_col);
                      goto e_failed;
                   }
 
                   top->type = json_double;
-                  top->u.dbl = (double) top->u.integer;
+                  top->u.dbl = dbl;
 
                   flags |= flag_num_got_decimal;
                   num_digits = 0;
@@ -847,8 +849,9 @@ json_value * json_parse_ex (json_settings * settings,
 
                      if (top->type == json_integer)
                      {
+                        double dbl = (double) top->u.integer;
                         top->type = json_double;
-                        top->u.dbl = (double) top->u.integer;
+                        top->u.dbl = dbl;
                      }
 
                      num_digits = 0;