[sdcc-devel] [ sdcc-Bugs-1444425 ] onebyte.c regression tes fails on pic16

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Bugs item #1444425, was opened at 2006-03-06 21:07
Message generated for change (Comment added) made by tecodev
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Category: pic16 target
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Borut Razem (borutr)
Assigned to: Raphael Neider (tecodev)
Summary: onebyte.c regression tes fails on pic16

Initial Comment:
1 - sample code:
------------------------
void main(void)
{
  char cL;
  volatile char cR;
  volatile char r16;

  cL = -1;
  cR = 1;
  r16 =  cL * cR;
}
------------------------

2 - sdcc command:
>sdcc -mpic16 -S t.c

3 - sdcc version:
>sdcc -v
SDCC :
mcs51/gbz80/z80/avr/ds390/pic16/pic14/TININative/xa51/ds400/hc08
2.5.4 #1216 (Mar  5 2006) (MINGW32)

4 - error message:
Internal error: validateOpType failed in
OP_SYMBOL(IC_LEFT(ic)) @ main.c:918: expected symbol,
got value

This code is extracted from onebyte.c regression test.

Borut


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>Comment By: Raphael Neider (tecodev)
Date: 2006-06-06 06:34

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Hmm, the given example is void: neither can -150 be
represented in 8 bit using 2's complement nor is -300=112
(mod 256).
It should read: -100 * 4 = -400 = 112 (mod 256).
The conclusions remain the same, though.

Probably multiplication should always be defined as an N x N
-> 2N bit operation (except for long, obviously) and the
result be cropped as required?

Raphael

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Comment By: Raphael Neider (tecodev)
Date: 2006-06-05 21:50

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I wonder why SDCC tried to multiply two signed chars here...
Should it not promote them to int first, as the result is 16
bit wide (hm, possibly promotion rules apply only to input
operands?)!?
-150 * 2 should be -300, but will yield -144=112 with the
current _mulschar: s8 x s8 -> s8.
Sign-extending the result to 16 bit does not suffice (MSB is
clear)... Modifying _mulschar's signature to s8 x s8 -> s16
would help, but it is not curerntly declared so.

Am I wrong? Is SDCC wrong? How I hate promotion ;-)
If I were to implement _mulschar: s8 x s8 -> s8, would I
have to throw away the upper byte and sign-extend the result
or can I use the unsigned case, which produces a correct 16
bit wide result! Or do we have to clip u8 x u8 -> u16 to 8
bits and clear the upper byte as well?!?

Hoping for illumination,
Raphael


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Comment By: Borut Razem (borutr)
Date: 2006-05-21 10:43

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Now the linker displays the folowing error:
error: missing definition for symbol "__mulschar", required
by "t.o"

The following code compiles without errors:

void main(void)
{
  volatile char cL;
  volatile char cR;
  volatile char r16;

  cL = -1;
  cR = 1;
  r16 =  cL * cR;
}

It uses the "MOVFF PRODL, _main_r16_1_1" istruction for
multiplication. The same approach should be probably used
for the failing case.

Borut


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Comment By: Raphael Neider (tecodev)
Date: 2006-03-08 10:00

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Fixed in src/pic16/main.c 1.68, SDCC #1221.

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