Assertion failed: Full-residue == 3^nsquares (mod q) check fails!

[efvb]

I am using code from main, May 5th, compiled with GCC 11 with tuned Makefile with -O3 -flto=auto -DUSE_ARM_V8_SIMD -mcpu=neoverse-n1
This is an Ampere Arm VM.

I also have the file to restart, if needed.

Mlucas 21.0.1

https://www.mersenneforum.org/mayer/README.html

INFO: testing qfloat routines...
System total RAM = 23236, free RAM = 10691
INFO: 10691 MB of free system RAM detected.
CPU Family = ARM Embedded ABI, OS = Linux, 64-bit Version, compiled with Gnu C [or other compatible], Version 11.4.1 20230605 (Red Hat 11.4.1-2.1.0.1).
INFO: Build uses ARMv8 advanced-SIMD instruction set.
INFO: Using prefetch.
INFO: Using inline-macro form of MUL_LOHI64.
INFO: Using FMADD-based 100-bit modmul routines for factoring.
INFO: MLUCAS_PATH is set to ""
INFO: using 53-bit-significand form of floating-double rounding constant for scalar-mode DNINT emulation.
INFO: testing IMUL routines...
INFO: Testing 64-bit 2^p (mod q) functions with 100000 random (p, q odd) pairs...
INFO: System has 4 available processor cores.
INFO: testing FFT radix tables...
Set affinity for the following 4 cores: 0.1.2.3.
User did not set LowMem in mlucas.ini ... allowing all test types.
User did not set CheckInterval in mlucas.ini ... using default.
NTHREADS = 4
Setting ITERS_BETWEEN_CHECKPOINTS = 10000.
looking for worktodo.txt file...
worktodo.txt file found...reading next assignment...
worktodo.txt entry: PRP=164C2E2861CC217CF6033B299322924C,1,2,8546743,-1,99,0,3,5,"209104614239,2707424768671102639169"

INFO: Maximum recommended exponent for FFT length (448 Kdbl) = 8954601; p[ = 8546743]/pmax_rec = 0.9544526886.
Initial DWT-multipliers chain length = [long] in carry step.
INFO: restart file p8546743 found...reading...
Computing 8540000-squaring residue R (mod known prime q = 209104614239)
A: R == 9997626983 (mod q)
B: R == 135567088145 (mod q)
ERROR: at line 5271 of file ../src/Mlucas.c
Assertion failed: Full-residue == 3^nsquares (mod q) check fails!

[tdulcet]

Thanks for the bug report!

There are some known issues with LTO (see #10), so would you mind disabling it so we can rule that out. Just remove the -flto=auto argument from your Makefile and then recompile Mlucas.

If that does not help, could you add this printf call:

printf("pow[0] = %llu\npow[1] = %llu\npow[2] = %llu\npow[3] = %llu\n\nrem[0] = %llu\nrem[1] = %llu\nrem[2] = %llu\nrem[3] = %llu\n\nk = %u\n", pow[0], pow[1], pow[2], pow[3], rem[0], rem[1], rem[2], rem[3], k);

above that assert statement on line 5271:

Mlucas/src/Mlucas.c

Lines 5268 to 5271 in 1839858

	// Raise 3 to the just-computed power; result in 4-limb local-array pow[]:
	mi64_scalar_modpow_lr(3ull, exp, KNOWN_FACTORS+i, j, pow);
	sprintf(cstr,"\tB: R == %s (mod q)\n",&cbuf[convert_mi64_base10_char(cbuf, pow, j, 0)] ); mlucas_fprint(cstr,1);
	ASSERT(HERE, mi64_getlen(pow,4) == k && mi64_cmp_eq(pow,rem,k), "Full-residue == 3^nsquares (mod q) check fails!");

and then recompile Mlucas. This would provide more information about why the assert statement is failing.

[Artoria2e5]

Looks like LTO thing got fixed. Always sneaky, those operand and clobber settings...