Subject:
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RE: h8/300 16-bit multiply
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Mon, 4 Mar 2002 05:26:52 GMT
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Reply-To:
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<rhempel@bmts#spamcake#.com>
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Viewed:
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2820 times
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> I'm trying to implement a 16bit multiply that leaves a 32bit result
> on the H8/300. The RCX ROM includes 16x16=16 and 32x32=32
> multiplication routines, but not the intermediate step. Any hints
> or pointers?
The easiest thing is to cast your 16 bit values to 32 bits and use the
built-in 32x32 multiply...
Here's the code from pbForth that does it. (It's written in a pseudo-
assebler, but you can probably figure it out...)
#------------------------------------------------------------------------------
# UM* UM* ( u1 u2 -- ud )
# ---------------------------------------------------------------------------
pbPrimary {UM*} UMStar 0 CORE
pbCode {} {MOV.W r3,rA } {Save the registers we're using}
pbCode {} {MOV.W r4,rB } { }
pbCode {} {MOV.W r5,rC } { }
pbCode {} {MOV.W #0x0000,r5 } {MSW of u2 }
pbCode {} {MOV.W @rDSP,r4 } {u1 }
pbCode {} {MOV.W #0x0000,r3 } {MSW of u1 }
pbCode {} {JSR _rom_ulong_mul } { }
pbCode {} {MOV.W r6,@rDSP } {LSW of ud }
pbCode {} {MOV.W r5,r6 } {MSW of ud }
pbCode {} {MOV.W rC,r5 } {Restore the registers we saved}
pbCode {} {MOV.W rB,r4 } { }
pbCode {} {MOV.W rA,r3 } { }
pbCode {} {JMP NEXT }
Cheers, Ralph
--------------------------------------------------------------------
Check out pbFORTH for LEGO Mindstorms at:
<http://www.hempeldesigngroup.com/lego/pbForth>
Buy "Extreme Mindstorms: an Advanced Guide to Lego Mindstorms"
<http://www.amazon.com/exec/obidos/ASIN/1893115844/hempeldesigngrou>
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Reply to: rhempel at bmts dot com
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Message has 1 Reply:
 | | Re: h8/300 16-bit multiply
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| Thanks. I have a version just 2 words longer that doesn't use the ROM code. Basically it's the ROM's code, trimmed down after assuming high words are zero initially. It's completely untested though, so there may be a bug. CODE UM* \ 16x16=32 (...) (23 years ago, 4-Mar-02, to lugnet.robotics.rcx)
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Message is in Reply To:
| | h8/300 16-bit multiply
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| I'm trying to implement a 16bit multiply that leaves a 32bit result on the H8/300. The RCX ROM includes 16x16=16 and 32x32=32 multiplication routines, but not the intermediate step. Any hints or pointers? (it should be straightforward, but my eyes (...) (23 years ago, 27-Feb-02, to lugnet.robotics.rcx)
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