base float buflen on float.h, not hardcoded assumptions

c_src/encoder.c

@@ -11,6 +11,8 @@
 
 #define BIN_INC_SIZE 2048
 
+#define FLOAT_BUFLEN (LDBL_DIG*2)
+
 #define MIN(X, Y) ((X) < (Y) ? (X) : (Y))
 
 #define MAYBE_PRETTY(e)             \
@@ -396,17 +398,17 @@ enc_double(Encoder* e, double val)
     size_t len;
     size_t i;
 
-    if(!enc_ensure(e, 32)) {
+    if(!enc_ensure(e, FLOAT_BUFLEN)) {
         return 0;
     }
 
     start = &(e->p[e->i]);
 
     // try to encode doubles using the fewest digits possible...
-    if (snprintf(start, 32, "%.*g", DBL_DIG, val) > FLT_DIG)
+    if (snprintf(start, FLOAT_BUFLEN, "%.*g", DBL_DIG, val) > FLT_DIG)
     {
         // ...fall back to full expansion to be safe
-        snprintf(start, 32, "%.*g", LDBL_DIG, val);
+        snprintf(start, FLOAT_BUFLEN, "%.*g", LDBL_DIG, val);
     }
     len = strlen(start);
 
@@ -416,7 +418,7 @@ enc_double(Encoder* e, double val)
             goto done;
     }
 
-    if(len > 29) return 0;
+    if(len >= FLOAT_BUFLEN-2) return 0;
 
     // Force a decimal point
     start[len++] = '.';