result in DEST. SRC should not be negative.
EMACS_SUB_TIME (DEST, SRC1, SRC2) subtracts SRC2 from SRC1 and
- stores the result in DEST. SRC should not be negative.
+ stores the result in DEST. SRC should not be negative.
EMACS_TIME_NEG_P (TIME) is true iff TIME is negative.
*/