What is the interger arithmetic overflow behavior with CUDA PTX?












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What happens when you add two b-bit integer values in CUDA, with the add PTX instruction rather than add.cc, add.c or add.sat, but their sum requires b+1 bits? I'm interested in both the signed and unsigned cases.



Similarly, what happens when you subtract two unsigned values with the latter lower than the former? Or subtract two negative b-bit signed integers, with the result requiring b+1 bits?



The PTX reference doesn't say. Is it like "undefined behavior" in C++, and we're not allowed to make any assumptions about it? Does it follow some per-uarch rule? Some global rule?



Notes:




  • A related question: How do I check for overflow of integer arithmetic in CUDA?










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    0














    What happens when you add two b-bit integer values in CUDA, with the add PTX instruction rather than add.cc, add.c or add.sat, but their sum requires b+1 bits? I'm interested in both the signed and unsigned cases.



    Similarly, what happens when you subtract two unsigned values with the latter lower than the former? Or subtract two negative b-bit signed integers, with the result requiring b+1 bits?



    The PTX reference doesn't say. Is it like "undefined behavior" in C++, and we're not allowed to make any assumptions about it? Does it follow some per-uarch rule? Some global rule?



    Notes:




    • A related question: How do I check for overflow of integer arithmetic in CUDA?










    share|improve this question

























      0












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      0







      What happens when you add two b-bit integer values in CUDA, with the add PTX instruction rather than add.cc, add.c or add.sat, but their sum requires b+1 bits? I'm interested in both the signed and unsigned cases.



      Similarly, what happens when you subtract two unsigned values with the latter lower than the former? Or subtract two negative b-bit signed integers, with the result requiring b+1 bits?



      The PTX reference doesn't say. Is it like "undefined behavior" in C++, and we're not allowed to make any assumptions about it? Does it follow some per-uarch rule? Some global rule?



      Notes:




      • A related question: How do I check for overflow of integer arithmetic in CUDA?










      share|improve this question













      What happens when you add two b-bit integer values in CUDA, with the add PTX instruction rather than add.cc, add.c or add.sat, but their sum requires b+1 bits? I'm interested in both the signed and unsigned cases.



      Similarly, what happens when you subtract two unsigned values with the latter lower than the former? Or subtract two negative b-bit signed integers, with the result requiring b+1 bits?



      The PTX reference doesn't say. Is it like "undefined behavior" in C++, and we're not allowed to make any assumptions about it? Does it follow some per-uarch rule? Some global rule?



      Notes:




      • A related question: How do I check for overflow of integer arithmetic in CUDA?







      cuda language-lawyer integer-overflow integer-arithmetic ptx






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      share|improve this question











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      share|improve this question










      asked Dec 27 '18 at 19:57









      einpoklum

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      33.4k26120234
























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