6.1.0705
ALIGN
 
CORE
 
( -- )

If the data-space pointer is not aligned, reserve enough space to align it.

See:
3.3.3 Data space, 3.3.3.1 Address alignment, A.6.1.0705 ALIGN.

Rationale:
In this standard we have attempted to provide transportability across various CPU architectures. One of the frequent causes of transportability problems is the requirement of cell-aligned addresses on some CPUs. On these systems, ALIGN and ALIGNED may be required to build and traverse data structures built with C,. Implementors may define these words as no-ops on systems for which they aren't functional.
Testing:
ALIGN 1 ALLOT HERE ALIGN HERE 3 CELLS ALLOT
CONSTANT A-ADDR CONSTANT UA-ADDR
T{ UA-ADDR ALIGNED -> A-ADDR }T
T{       1 A-ADDR C!         A-ADDR       C@ ->       1 }T
T{    1234 A-ADDR !          A-ADDR       @  ->    1234 }T
T{ 123 456 A-ADDR 2!         A-ADDR       2@ -> 123 456 }T
T{       2 A-ADDR CHAR+ C!   A-ADDR CHAR+ C@ ->       2 }T
T{       3 A-ADDR CELL+ C!   A-ADDR CELL+ C@ ->       3 }T
T{    1234 A-ADDR CELL+ !    A-ADDR CELL+ @  ->    1234 }T
T{ 123 456 A-ADDR CELL+ 2!   A-ADDR CELL+ 2@ -> 123 456 }T