F33 Error Solved: 'ierr < ERR_MAX' Explained

by Luna Greco 45 views

Hey everyone! Today, we're diving deep into a rather cryptic error that some users have encountered while running P-1 stage 2 on F33. Specifically, the error message reads: Assertion 'ierr < ERR_MAX' failed: Error code out of range! This error popped up for Ken on the Mersenne Forum, and it seems to be affecting users with AVX512 systems using GCC 13.3. Let's break down what this means, why it's happening, and what we can potentially do about it.

Understanding the Error: Assertion 'ierr < ERR_MAX' Failed

What Does This Error Message Mean?

When you encounter the frustrating error message "Assertion 'ierr < ERR_MAX' failed: Error code out of range!", it indicates a critical issue within the Mlucas library, particularly during the P-1 stage 2 computation. This assertion failure signifies that the error code (ierr) generated by the Mlucas functions has exceeded the maximum permissible value defined by ERR_MAX. In simpler terms, something went wrong during the calculation, and the error code produced doesn't fit within the expected range, suggesting a severe and unexpected problem.

This kind of error often points to a deeper underlying issue, such as a bug in the code, memory corruption, or hardware incompatibility. To effectively troubleshoot it, it's essential to understand the context in which the error occurs. In this case, it surfaces when running P-1 stage 2 on F33, especially on systems with AVX512 and GCC 13.3. This context helps narrow down the potential causes and guides the debugging process.

The Context: P-1 Stage 2 and F33

To truly grasp the significance of this error, let's first understand the context in which it occurs. The error arises during the P-1 stage 2 of the Mlucas primality test, a crucial phase in determining whether a given number is prime. The P-1 method itself is a powerful algorithm designed to identify prime numbers by leveraging the factorization properties of numbers one less than the potential prime. Stage 2 is a refined step in this process, intended to catch primes that might slip through the initial checks.

F33 refers to a specific number or modulus being tested for primality. In this context, it’s a large number that requires significant computational resources to analyze. The complexity of handling such large numbers means that even minor issues in the code or system can lead to errors like the one we're discussing. Additionally, the fact that this error is reported on systems using AVX512 instruction sets and the GCC 13.3 compiler suggests a possible interaction or incompatibility with these specific technologies.

Diving into the Code: MlUCAS and Error Codes

Now, let’s delve a bit deeper into the code to understand where this error originates. The error message points to the Mlucas library, which is a core component in prime number testing and related computations. Specifically, the message ERROR: Function returnMlucasErrCode, at line 4903 of file ../src/Mlucas.c pinpoints the exact location in the Mlucas source code where the error occurs.

In Mlucas, error handling is managed through a system of error codes. These codes are integer values that represent different types of issues encountered during computation. The library defines a maximum error code, ERR_MAX, and when an error occurs that produces a code exceeding this limit, the assertion failure is triggered. This mechanism is in place to ensure that errors are properly managed and don't lead to unpredictable behavior or incorrect results.

The specific error code 20, mentioned in the original report, is suspected to be a combination of two ERR_CARRY errors, each with a value of 10. The ERR_CARRY error typically indicates an overflow or carry issue during arithmetic operations, which is a common concern when dealing with very large numbers in primality testing. Understanding these error codes and their context within the Mlucas library is crucial for effectively diagnosing and resolving the problem.

AVX512 and GCC 13.3: Potential Culprits?

One of the key observations in the error report is that this issue seems to occur predominantly on systems using AVX512 instruction sets and compiled with GCC 13.3. This narrows down the potential causes to a few key areas:

  1. AVX512 Instruction Set: AVX512 is an advanced set of instructions that allows CPUs to perform operations on larger chunks of data simultaneously, significantly speeding up certain types of computations. However, these advanced instructions can sometimes expose bugs in code that are not apparent in simpler instruction sets. There might be an issue in how Mlucas utilizes AVX512, or a hardware-level problem with the AVX512 implementation on specific processors.

  2. GCC 13.3 Compiler: The GCC compiler is responsible for translating human-readable code into machine-executable instructions. Compilers can introduce bugs or generate code that behaves unexpectedly under certain conditions. It’s possible that GCC 13.3 has a bug that affects the compiled Mlucas code, especially when AVX512 instructions are involved. Compiler optimizations, while generally beneficial, can sometimes lead to subtle errors that are hard to trace.

  3. Interaction between AVX512 and GCC 13.3: It’s also possible that the issue is not with either AVX512 or GCC 13.3 in isolation but rather with their interaction. The way GCC 13.3 generates AVX512 instructions for Mlucas might be the source of the problem. This type of interaction bug can be particularly challenging to diagnose.

To address these potential culprits, it may be necessary to test Mlucas with different compilers (e.g., older versions of GCC or other compilers like Clang) and on systems with and without AVX512. This would help isolate the specific conditions under which the error occurs and provide valuable clues for developers to fix the issue.

Decoding the Technical Details: A Closer Look

Worktodo.txt Entry

Alright, let's break down the worktodo.txt entry. This file likely contains instructions for the Mlucas software, telling it what kind of primality test to run. The entry:

Pminus1=1,2,8589934592,+1,10000000,900000000,96,800000000

This line specifies a P-1 test (that's the Pminus1=1). Let's dissect the other values:

  • 2,8589934592: This is likely the base and the number we're testing (N). So, we're testing 8589934592 for primality using base 2.
  • +1: This could be a flag or parameter, possibly indicating a specific variation of the P-1 test.
  • 10000000: This is B1, the bound for Stage 1. Stage 1 checks for prime factors up to this limit.
  • 900000000: This is B2, the upper bound for Stage 2. Stage 2 checks for larger prime factors between B2_start and B2.
  • 96: This is likely a thread count or related parameter.
  • 800000000: This is B2_start, the lower bound for Stage 2.

So, in a nutshell, we're running a P-1 test on 8589934592, with Stage 1 checking primes up to 10,000,000 and Stage 2 checking between 800,000,000 and 900,000,000.

Log File Analysis

Now, let's dissect the log output. It's a goldmine of information! Here are some key takeaways: