[RFCv2 1/2] Add new defer word for mu/mod to allow division behaviour to be customised on a per platform basis.

[Mark Cave-Ayland]

Signed-off-by: Mark Cave-Ayland 
---
 openbios-devel/forth/bootstrap/bootstrap.fs |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/openbios-devel/forth/bootstrap/bootstrap.fs b/openbios-devel/forth/bootstrap/bootstrap.fs
index 6878449..ded2e90 100644
--- a/openbios-devel/forth/bootstrap/bootstrap.fs
+++ b/openbios-devel/forth/bootstrap/bootstrap.fs
@@ -445,10 +445,15 @@ variable leaves 0 leaves !
 \ 7.3.2.3 double number arithmetic
 \

+defer (mu/mod)
+
 : s>d      dup 0 < ; 
 : dnegate  0 0 2swap d- ;
 : dabs     dup 0 < if dnegate then ;
-: um/mod   mu/mod drop ;
+: um/mod   (mu/mod) drop ;
+
+\ default divide implementation
+['] mu/mod ['] (mu/mod) (to)

\ symmetric division
 : sm/rem  ( d n -- rem quot )

[RFCv2 2/2] PPC: Mimic Apple's OpenFirmware behaviour if a divide by zero occurs.

[Mark Cave-Ayland]

As reported by Amadeusz Sławiński using a real Mac, if anything is divided by
zero then we should return zero:

0 > 2 0 /  ok
1 > u. 0  ok

This resolves a bug in BootX which (un)intentionally divides by zero during
boot.

Signed-off-by: Mark Cave-Ayland 
---
 openbios-devel/arch/ppc/ppc.fs |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/openbios-devel/arch/ppc/ppc.fs b/openbios-devel/arch/ppc/ppc.fs
index 6995ba9..e07765b 100644
--- a/openbios-devel/arch/ppc/ppc.fs
+++ b/openbios-devel/arch/ppc/ppc.fs
@@ -55,3 +55,23 @@

\ Set by BootX when booting Mac OS X
 defer spin
+
+\ BootX has a bug whereby it divides by zero when booting from any device
+\ other than the network (see openbios list archive for details). The
+\ behaviour on real hardware is for the trap to "catch" the exception and
+\ then continue.
+\
+\ Since OpenBIOS PPC can't trap into Forth, we emulate this behaviour by
+\ checking for divide by zero and returning the same result as real hardware
+\ which is a single zero e.g.
+\
+\ 0 > 2 0 /  ok
+\ 1 > u. 0  ok
+
+:noname
+  dup 0= if
+    3drop 0 0 0
+  else
+    mu/mod
+  then
+; to (mu/mod)