Compiler/UCD3138: two 32-bits data multiplication result is not correct

Prodigy 470 points

Julie Zhu

Part Number: UCD3138

Tool/software: TI C/C++ Compiler

Hi,

I am using CCS6.1 with compiler 5.22. I found the result of multiplication of two 32-bits data is not correct.  I defined the result as 64 bits data. the correct result should be 0x0000 0056  0038 7512. I saw one register R0 has the number 0x0000 0056, another register R1 has the number 0x00387512,  which is correct. however, the result I get is 0x0038 7512 0000 0056, which seems the two registers's data are put in the wrong order.

Is it a bug or I didn't configure the CCS correctly?

Thanks,

Julie

Prodigy 470 points

Julie Zhu

• May 10, 2017 2:15 PM
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18 Replies

• Genius 4945 points

  

  Keith Barkley

  

  • May 10, 2017 2:56 PM

  Can you show your code snippet?

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  Julie Zhu

  

  • May 10, 2017 4:00 PM

  In reply to Keith Barkley:

  the code is :

  Uint16 uint16_multiply_shift_clamp(Uint32 x, Uint32 y, int16 shift, Uint16 max_value)
  {
  Uint64 scale_product_64;

  scale_product_64 = (Uint64)x*y;

  .............

  }

  I tried to declare the variable scale_product_64 as a global variable, then the result is correct. 

  please refer to attached document.  I put all the screen captures into this document. 

  

  Thanks

  Julie64-bits multiplication.docx

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• Genius 4945 points

  

  Keith Barkley

  

  • May 10, 2017 4:17 PM

  In reply to Julie Zhu:

  The question is are you casting x to uint64_t or x*y to uint64_t? IF the latter, the multiplication will still be 32 bit.
  Try ((uint64_t)x) * y

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• Prodigy 470 points

  

  Julie Zhu

  

  • May 10, 2017 4:26 PM

  In reply to Keith Barkley:

  I am pretty sure that is not the reason.
  
  first, I used the same statement for the case that scale_product_64 is declared as global variables. the result is correct.
  
  second, I tried different ways, like scale_product_64 = ((Uint64)x)*((Uint64)y); the result is same.
  
  but know I figure out it might just be a issue of displaying inside the debugger. I think the display has a bug that arrange the words in the wrong order.

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• Guru 128290 points

  

  George Mock

  

  • May 10, 2017 10:14 PM

  In reply to Julie Zhu:

  This is expected behavior.  When a 64-bit integer value resides in a register pair, the even register holds the high order bits, and the odd register holds the low order bits.  When inspecting 64-bit values, avoid looking at the registers.  It is easy to get confused.  Look in the watch window, or something similar.

  Thanks and regards,

  -George

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• Expert 1660 points

  

  Markus Moll

  

  • May 11, 2017 7:17 AM

  In reply to George Mock:

  George Mock

  This is expected behavior.  When a 64-bit integer value resides in a register pair, the even register holds the high order bits, and the odd register holds the low order bits.  When inspecting 64-bit values, avoid looking at the registers.  It is easy to get confused.  Look in the watch window, or something similar.

  I think Julie gave an example where the watch window would show a wrong 64 bit value (namely, when the variable was stored in a register rather than in memory). That looks like a bug in CCS to me (not in the compiler, though).

  Markus

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  Julie Zhu

  

  • May 11, 2017 3:00 PM

  In reply to Markus Moll:

  George,

  If you look at the screen capture I provided, the data shown in the watch window is in wrong order when it arranges the 64-bits data from 2 registers.  Should be a problem in the watch window display.

  Julie

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• Guru 58285 points

  

  Chester Gillon

  

  • May 13, 2017 2:57 PM

  In reply to Julie Zhu:

  Julie Zhu

  If you look at the screen capture I provided, the data shown in the watch window is in wrong order when it arranges the 64-bits data from 2 registers.  Should be a problem in the watch window display.

  I tried to repeat the problem using the ARM9 core in a AM1808 using CCS 6.1.2.00014 and TI ARM compiler v5.2.0 (the closest versions to those you are using which I had installed). I couldn't repeat the problem, in that the sum 64-bit sum variable held in a register pair was displayed correctly in the variable view:

  

  In the above working example the 64-bit variable sum is given a register-pair location of "R8:32,R9:32" in the Variables view, whereas in your failure case the location is given as "R0" which is a single 32-bit register.

  Can you post an example project which shows the problem, along with the exact CCS version number? Not sure if the problem is either:

  a) A bug in the CCS version you are using.

  b) The debug information generated by the compiler has specified the wrong register location for the 64-bit scale_product_64 variable.

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  Julie Zhu

  

  • May 15, 2017 3:25 PM

  In reply to Chester Gillon:

  Hi, Chester,

  the CCS version I am using is Version: 6.1.0.00104.  the project is for UCD3138, I have attached the screen capture for the details.

  

  Julie

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  Chester Gillon

  

  • May 15, 2017 11:36 PM

  In reply to Julie Zhu:

  Julie Zhu

  the CCS version I am using is Version: 6.1.0.00104.  the project is for UCD3138, I have attached the screen capture for the details.

  Thanks for the information. I don't have that CCS version installed and don't have a UCD3138 so can't re-create the problem to investigate.

  Not sure if it is significant, but the UCD3138 is big-endian, whereas the ARM devices I failed to re-create the problem with are little-endian. Hopefully someone from TI can repeat the problem with a UCD3138.

  Are you able to try a later CCS version to see if the problem has been fixed in a later version?

  E.g. found Expressions and variables windows not displaying correct values which was reported against CCS  6.1.0.00104, for which bug SDSCM00051806 was raised which was fixed in CCS 6.1.1

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