[sdcc-devel] [ sdcc-Bugs-1064087 ] wrong compilation of adding chars

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Bugs item #1064087, was opened at 2004-11-10 20:57
Message generated for change (Comment added) made by scdgro77
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Category: msc51(8051) target
Group: non bugs
>Status: Open
Resolution: Rejected
Priority: 5
Submitted By: gerrit (scdgro77)
Assigned to: Nobody/Anonymous (nobody)
Summary: wrong compilation of adding chars

Initial Comment:
when i'm compiling the following line it produces wrong
output.

all vars are chars ! when they are integers, the
compiling produces the right output. So it goes wrong
with chars !

test = '0' + i2c_read_bytes; 

compiled with test and i2c_read_bytes as integers :

345 	mov	r4,_i2c_comm_PARM_3
347 	mov	a,#0x30
349 	add	a,r4
350 	mov	_i2c_comm_test_1_1,a

Wrong output  with  test and i2c_read_bytes as chars :

340 ;i2c.c:61: test = '0' + i2c_read_bytes; 
342 	mov	_i2c_comm_test_1_1,r3

See the file i2c.c for further details
Use the file  ./compile   to compile the stuff 

Platform is gentoo linux.
SDCC -v output :
mcs51/gbz80/z80/avr/ds390/pic16/pic14/TININative/xa51/ds400/hc08
2.4.2 (Oct 24 2004) (UNIX)

sc...@ne...


	

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>Comment By: gerrit (scdgro77)
Date: 2004-11-13 08:59

Message:
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@Epetrich, Sorry i have to critisize you but it seems you
haven't done your homework right (and would have closed the
bug too soon)
The C code remains the same, so in both cases, 1st where
i2c_read_bytes is declared as char, 2nd where i2c_read_bytes
declared as int, the compiler has to produce code where the
'0x30' is added, but it doesn't. In your words, with the
char, all is treated as a constant, and with the int, it's
treated as a variable. Futhermore, with the int my
application works, with the char it doesn't. But please read
the answer to maartenbrock also.

@Maartenbrock.
In 2.4.6 the compiler produces the output as expected, and
works with the char.


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Comment By: Erik Petrich (epetrich)
Date: 2004-11-13 08:34

Message:
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Although the compiler output may not be what you expected,
it appears to be correct to me. The compiler notices that
the expression '0' + i2c_read_bytes is constant over the
duration of the for loop and so computes the result before
the loop begins:

mov a,#0x30
add a,_i2x_comm_PARM_3
mov r3,a

(lines 314-316 in my copy of i2c.asm; your line numbers do
not exactly match with mine, due to version differences I
assume).

Within the loop, the only thing that remains to do is to
assign this result to the variable 'test':

mov _i2c_comm_test_1_1,r3


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Comment By: Maarten Brock (maartenbrock)
Date: 2004-11-11 08:51

Message:
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user_id=888171

Can you confirm that this still exists in version 2.4.6?

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