From 279a8b5800d971fe205308f5c753a53fd455611c Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Tue, 8 Apr 2025 15:28:16 -0700
Subject: New macros: mul and div.

* autoload.c (place_set_entries): Add mul and div
symbols as autoload triggers.

* stdlib/place.tl (mul, div): New macros.

* txr.1: Documented.
---
 autoload.c      |  2 +-
 stdlib/place.tl |  8 ++++++++
 txr.1           | 24 ++++++++++++++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/autoload.c b/autoload.c
index b666e386..377a54dd 100644
--- a/autoload.c
+++ b/autoload.c
@@ -101,7 +101,7 @@ static val place_set_entries(val fun)
     lit("with-update-expander"), lit("with-clobber-expander"),
     lit("with-delete-expander"),
     lit("set"), lit("pset"), lit("zap"), lit("flip"), lit("inc"), lit("dec"),
-    lit("pinc"), lit("pdec"),
+    lit("pinc"), lit("pdec"), lit("mul"), lit("div"),
     lit("set-mask"), lit("clear-mask"),
     lit("push"), lit("pop"), lit("swap"), lit("shift"), lit("rotate"),
     lit("test-set"), lit("test-clear"), lit("compare-swap"),
diff --git a/stdlib/place.tl b/stdlib/place.tl
index 993dd75c..cd6cbd9d 100644
--- a/stdlib/place.tl
+++ b/stdlib/place.tl
@@ -283,6 +283,14 @@
   (with-update-expander (getter setter) place env
     ^(,setter (logand (,getter) (lognot (logior ,*integers))))))
 
+(defmacro mul (place factor :env env)
+  (with-update-expander (getter setter) place env
+    ^(,setter (* (,getter) ,factor))))
+
+(defmacro div (place factor :env env)
+  (with-update-expander (getter setter) place env
+    ^(,setter (/ (,getter) ,factor))))
+
 (defmacro swap (place-0 place-1 :env env)
   (with-gensyms (tmp)
     (with-update-expander (getter-0 setter-0) place-0 env
diff --git a/txr.1 b/txr.1
index ebe010dc..508682b5 100644
--- a/txr.1
+++ b/txr.1
@@ -44944,6 +44944,30 @@ then
 is returned, otherwise
 .codn nil .
 
+.coNP Macros @ mul and @ div
+.synb
+.mets (mul << place < factor )
+.mets (div << place < factor )
+.syne
+.desc
+The
+.code mul
+and
+.code div
+macros update
+.meta place
+by scaling its value by
+.metn factor .
+
+The following equivalences hold, except that the operand
+.code x
+is evaluated only once:
+
+.verb
+  (mul x y)  <-->  (set x (* x y))
+  (div x y)  <-->  (set x (/ x y))
+.brev
+
 .coNP Macro @ swap
 .synb
 .mets (swap < left-place << right-place )
-- 
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