adding the AGAIN control word

[rrq/rrqforth.git] / adoc / p_0branch.adoc

diff --git a/adoc/p_0branch.adoc b/adoc/p_0branch.adoc
index 16c69c0249c115ab3cddd90a70a5b8f1b1107db7..6488d62ab6c305c4c421abd782609db3eaeab75a 100644 (file)
--- a/adoc/p_0branch.adoc
+++ b/adoc/p_0branch.adoc
@@ -1,9 +1,26 @@
-anchor:p_zero_branch[]
+// contorl.asm:        WORD p_zero_branch,'0BRANCH',fasm
 
-Word: 0BRANCH
--------------
+anchor:p_0branch[]
 
-----
-rrqforth.asm:  WORD p_zero_branch,'0BRANCH',fasm
-----
+=== Word: 0BRANCH
 
+....
+Data stack: ( v -- )
+....
+
+"0BRANCH" is a function word that implements execution conditional by
+means of optionally adding the subsequent branch offset, or not, to
+the point of execution. If the value, v, is 0 then the branch offset
+is added, and otherwise execution continues with the cell following
+the branch offset in the definition.
+
+Note that the branch offset is a byte count and each FORTH word of a
+definition take up a cell of 8 bytes. The offset is relative to the
+cell address immediately subsequent to the offset cell. In other
+words, offset 0 is not branching anywhere and an offset of -16 would
+make a tight loop back to the branch instruction itself. The latter
+would pull data stack values until and including the first non-zero
+value.
+
+See also <<p_1branch,1BRANCH>>, <<p_branch,BRANCH>>, <<p_if,IF>>,
+<<p_else,ELSE>>, <<p_ifbreak,IFBREAK>> and <<p_ifagain,IFAGAIN>>.