+/* Save a double value. Doubles are saved as strings prefixed by an unsigned
+ * 8 bit integer specifing the length of the representation.
+ * This 8 bit integer has special values in order to specify the following
+ * conditions:
+ * 253: not a number
+ * 254: + inf
+ * 255: - inf
+ */
+static int rdbSaveDoubleValue(FILE *fp, double val) {
+ unsigned char buf[128];
+ int len;
+
+ if (isnan(val)) {
+ buf[0] = 253;
+ len = 1;
+ } else if (!isfinite(val)) {
+ len = 1;
+ buf[0] = (val < 0) ? 255 : 254;
+ } else {
+ snprintf((char*)buf+1,sizeof(buf)-1,"%.16g",val);
+ buf[0] = strlen((char*)buf);
+ len = buf[0]+1;
+ }
+ if (fwrite(buf,len,1,fp) == 0) return -1;
+ return 0;
+}
+