On Thu, Aug 27, 2015 at 12:25 PM, Stuart Bishop stuart@stuartbishop.net wrote:

I have billions of rows of data in my databases. If I'm dealing with input from computer systems, such as my databases, I will have billions of conversions to do and the overhead of calculating the fold flag is billions of times worse than calculating the isdst flag from the non-bulk human input.

Do you realize that a typical portable implementation of mktime calls localtime up to four times to get tm_isdst? And to get it completely "right", needs up to six calls? [1] I am sure I can do no worse than that computing the fold value.

[1]: "BUG in mktime" https://www.sourceware.org/ml/libc-hacker/1998-10/msg00027.html