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Hi, I wonder if someone can help me. I'm pretty new to Codewarrior and the 56000, but am an experienced C programmer so I'm not completely clueless. However, I'm getting some behaviour from the compiler which seems a bit odd to me. I have a structure, one member of which is a long. I'm setting this to an initialisation value near the start of my program. This value is a constant multiplied by a Scaling factor, which I'm currently experimenting with. The scaling value is set by use of a #define in a header file. Its value is currently set to 250. So I have a line of code as follows: controls.slRelease = 200 * SCALEFACTOR; I was expecting the value of controls.slRelease to be 50,000, but it isn't - it's -15536. Looking at the assembly produced by the compiler, I get: 0x0000004C 0x86F40000C350 movei #-15536,X:0x0000 0x0000004F 0x86F40000FFFF movei #-1,X:0x0000 Looking at how longs are stored in memory, the first line of this, setting the low order word, is correct. The high order word, however, has been set to 0xFFFF, which isn't what I was expecting at all. To check, I got rid of the #define: controls.slRelease = 200 * 250; which produces the same compiler output. As a further test I wrote the value to the variable directly: controls.slRelease = 50000; The compiler produced the following: 0x00000052 0x86F40000C350 movei #-15536,X:0x0000 0x00000055 0x86F400000000 movei #0,X:0x0000 whch shows up as my expected value of 50,000. It seems that the compiler is treating the high order word in these cases differently. Is this what is happening, and if so why - what have I missed? Or have I found a bug? Thanks for your time Dave Falconer |
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Unexpected compiler result for maths on a long data type
Started by ●January 11, 2004
Reply by ●January 12, 20042004-01-12
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Hi Dave Is it possible that you have mis-matched declarations? Once I had somewhat similar behavior because I had defined a variable as unsigned long in one file and then (foolishly) had typed an extern declaration of the same variable as an unsigned short in another file. I used to think that a linker was guaranteed to catch such a bug and treat it as an error, but no. The resulting code was not what I had expected. If I recall, I was doing a modulus on the long (%) but it was being treated as a short. Rick Corey -----Original Message----- From: dtw_aerie [mailto:] Sent: Sunday, January 11, 2004 4:58 PM To: Subject: [motoroladsp] Unexpected compiler result for maths on a long data type Hi, I wonder if someone can help me. I'm pretty new to Codewarrior and the 56000, but am an experienced C programmer so I'm not completely clueless. However, I'm getting some behaviour from the compiler which seems a bit odd to me. I have a structure, one member of which is a long. I'm setting this to an initialisation value near the start of my program. This value is a constant multiplied by a Scaling factor, which I'm currently experimenting with. The scaling value is set by use of a #define in a header file. Its value is currently set to 250. So I have a line of code as follows: controls.slRelease = 200 * SCALEFACTOR; I was expecting the value of controls.slRelease to be 50,000, but it isn't - it's -15536. Looking at the assembly produced by the compiler, I get: 0x0000004C 0x86F40000C350 movei #-15536,X:0x0000 0x0000004F 0x86F40000FFFF movei #-1,X:0x0000 Looking at how longs are stored in memory, the first line of this, setting the low order word, is correct. The high order word, however, has been set to 0xFFFF, which isn't what I was expecting at all. To check, I got rid of the #define: controls.slRelease = 200 * 250; which produces the same compiler output. As a further test I wrote the value to the variable directly: controls.slRelease = 50000; The compiler produced the following: 0x00000052 0x86F40000C350 movei #-15536,X:0x0000 0x00000055 0x86F400000000 movei #0,X:0x0000 whch shows up as my expected value of 50,000. It seems that the compiler is treating the high order word in these cases differently. Is this what is happening, and if so why - what have I missed? Or have I found a bug? Thanks for your time Dave Falconer _____________________________________ Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. _____________________________________ About this discussion group: To Join: To Post: To Leave: Archives: http://www.yahoogroups.com/group/motoroladsp More Groups: http://www.dsprelated.com/groups.php3 |
Reply by ●January 12, 20042004-01-12
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Hi Dave, You must use: controls.slRelease = (long) 200 * SCALEFACTOR; or controls.slRelease = 200 * (long) SCALEFACTOR; otherwise the compiler thinks that you mean: controls.slRelease = (long) (int) 200 * SCALEFACTOR; that delivers: (long) (int) 50000 that is: (long) -15536 in your special case (there will yet be no overflow) you can also use (but I don't advice it): controls.slRelease = (long) (unsigned) (200 * SCALEFACTOR); kind regards, Wim de Haan Exendis B.V. W.J. de Haan P.O.box 56, 6710 BB Ede Keesomstraat 4, 6716 AB Ede The Netherlands. Tel: +31-(0)318 - 676305 Fax: +31-(0)318 - 676319 mailto: URL: http://www.exendis.com <http://www.exendis.com/ -----Original Message----- From: dtw_aerie [mailto:] Sent: zondag 11 januari 2004 22:58 To: Subject: [motoroladsp] Unexpected compiler result for maths on a long data type Hi, I wonder if someone can help me. I'm pretty new to Codewarrior and the 56000, but am an experienced C programmer so I'm not completely clueless. However, I'm getting some behaviour from the compiler which seems a bit odd to me. I have a structure, one member of which is a long. I'm setting this to an initialisation value near the start of my program. This value is a constant multiplied by a Scaling factor, which I'm currently experimenting with. The scaling value is set by use of a #define in a header file. Its value is currently set to 250. So I have a line of code as follows: controls.slRelease = 200 * SCALEFACTOR; I was expecting the value of controls.slRelease to be 50,000, but it isn't - it's -15536. Looking at the assembly produced by the compiler, I get: 0x0000004C 0x86F40000C350 movei #-15536,X:0x0000 0x0000004F 0x86F40000FFFF movei #-1,X:0x0000 Looking at how longs are stored in memory, the first line of this, setting the low order word, is correct. The high order word, however, has been set to 0xFFFF, which isn't what I was expecting at all. To check, I got rid of the #define: controls.slRelease = 200 * 250; which produces the same compiler output. As a further test I wrote the value to the variable directly: controls.slRelease = 50000; The compiler produced the following: 0x00000052 0x86F40000C350 movei #-15536,X:0x0000 0x00000055 0x86F400000000 movei #0,X:0x0000 whch shows up as my expected value of 50,000. It seems that the compiler is treating the high order word in these cases differently. Is this what is happening, and if so why - what have I missed? Or have I found a bug? Thanks for your time Dave Falconer _____________________________________ Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. _____________________________________ About this discussion group: To Join: To Post: To Leave: Archives: http://www.yahoogroups.com/group/motoroladsp <http://www.yahoogroups.com/group/motoroladsp> More Groups: http://www.dsprelated.com/groups.php3 <http://www.dsprelated.com/groups.php3 <http://rd.yahoo.com/SIGc4hkk48/M&7637.4116732.5333197.1261774/D=egroup web/S05771855:HM/EXP73997778/A53619/R=0/*http://www.netflix.com/Def ault?mqso`178356&partidA16732> click here <http://us.adserver.yahoo.com/l?M&7637.4116732.5333197.1261774/D=egroupmai l/S=:HM/A53619/rand1026647 _____ > . |
Reply by ●January 12, 20042004-01-12
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Hi Dave, You must use: controls.slRelease = (long) 200 * SCALEFACTOR; or controls.slRelease = 200 * (long) SCALEFACTOR; otherwise the compiler thinks that you mean: controls.slRelease = (long) (int) (200 * SCALEFACTOR) ; // Sorry I forgot ( ) in my first E-mail that delivers: (long) (int) 50000 that is: (long) -15536 in your special case (there will yet be no overflow) you can also use (but I don't advice it): controls.slRelease = (long) (unsigned) (200 * SCALEFACTOR); kind regards, Wim de Haan Exendis B.V. W.J. de Haan P.O.box 56, 6710 BB Ede Keesomstraat 4, 6716 AB Ede The Netherlands. Tel: +31-(0)318 - 676305 Fax: +31-(0)318 - 676319 mailto: URL: http://www.exendis.com <http://www.exendis.com/ -----Original Message----- From: dtw_aerie [mailto:] Sent: zondag 11 januari 2004 22:58 To: Subject: [motoroladsp] Unexpected compiler result for maths on a long data type Hi, I wonder if someone can help me. I'm pretty new to Codewarrior and the 56000, but am an experienced C programmer so I'm not completely clueless. However, I'm getting some behaviour from the compiler which seems a bit odd to me. I have a structure, one member of which is a long. I'm setting this to an initialisation value near the start of my program. This value is a constant multiplied by a Scaling factor, which I'm currently experimenting with. The scaling value is set by use of a #define in a header file. Its value is currently set to 250. So I have a line of code as follows: controls.slRelease = 200 * SCALEFACTOR; I was expecting the value of controls.slRelease to be 50,000, but it isn't - it's -15536. Looking at the assembly produced by the compiler, I get: 0x0000004C 0x86F40000C350 movei #-15536,X:0x0000 0x0000004F 0x86F40000FFFF movei #-1,X:0x0000 Looking at how longs are stored in memory, the first line of this, setting the low order word, is correct. The high order word, however, has been set to 0xFFFF, which isn't what I was expecting at all. To check, I got rid of the #define: controls.slRelease = 200 * 250; which produces the same compiler output. As a further test I wrote the value to the variable directly: controls.slRelease = 50000; The compiler produced the following: 0x00000052 0x86F40000C350 movei #-15536,X:0x0000 0x00000055 0x86F400000000 movei #0,X:0x0000 whch shows up as my expected value of 50,000. It seems that the compiler is treating the high order word in these cases differently. Is this what is happening, and if so why - what have I missed? Or have I found a bug? Thanks for your time Dave Falconer |
