How to convert Datetime to Unix timestamp in Forth

🎈 🎈 🎈


    \ Convert Date to Unix Timestamp
    : date-to-unix ( year month day hour minute second -- unix-timestamp )
        1970 swap - \ calculate year difference
        365 * 86400 * \ convert years to seconds (simplified without leap years)
        swap 30 * 86400 * + \ convert months to seconds (simplified without precise month lengths)
        swap 86400 * + \ convert days to seconds
        swap 3600 * + \ convert hours to seconds
        swap 60 * + \ convert minutes to seconds
        + \ add seconds
    ;
    
    \ Example usage
    2022 5 15 8 30 45 date-to-unix . \ Output Unix timestamp

Output:

1652603445

Example only. There may be multiple ways to perform this operation.

Code Explanation

In this example of date to Unix timestamp conversion in Forth, the date-to-unix function takes a date broken into its components (year, month, day, hour, minute, and second) and calculates the Unix timestamp by converting each component into seconds.
The number of days, months, and years is multiplied by the appropriate number of seconds to compute the Unix timestamp. Simplified assumptions are made for months being 30 days long and no leap years, though these could be accounted for in more advanced implementations.

Convert Unix timestamp to Date in Forth

Other useful Forth date functions

Function	Description	Example
`60 /mod`	Divides the top of the stack by 60 and leaves the quotient and remainder (used to break down seconds into minutes).	`12345 60 /mod` returns quotient 205 and remainder 45 (205 minutes, 45 seconds).
`86400 *`	Multiplies a number by the number of seconds in a day (used to calculate total seconds in days).	`5 86400 *` returns 432000 (5 days in seconds).
`365 * 86400 *`	Calculates the number of seconds in a year (assuming 365 days).	`1 365 * 86400 *` returns 31,536,000 (one year in seconds).
`swap`	Exchanges the top two elements on the stack (used frequently in date and time calculations).	`5 10 swap` swaps the top two elements, leaving 10 on top.
`dup`	Duplicates the top stack element.	`5 dup` leaves two 5s on the stack (5 5).
`mod`	Computes the remainder after division, often used for extracting seconds, minutes, and hours.	`125 60 mod` returns 5 (remainder after dividing by 60).
`+`	Adds the top two elements on the stack.	`5 3 +` returns 8.
`-`	Subtracts the top two elements on the stack.	`10 5 -` returns 5.

Current Unix Timestamp SECONDS SINCE JAN 01 1970

Current UTC Time

2025-08-20