GMPECM vs mprime for F12?
I've been playing a bit with GMPECM vs. mprime for the remaining C1133 of F12.
It seems mprime's ECM mode is way faster (3 hours vs. 6+) on my Xeon. Why is this? Does it have some particular optimizations for Fermat numbers, the use of gwnum, something else? 
Yes, mprime uses the faster gwnum library vs. GMP for GMPECM.
However, GMPECM uses a superior algorithm for stage 2. So, the optimal solution is to use mprime for stage 1 and GMPECM for stage 2. Dig around in the forums for instructions on how to do this. Good luck in your search 
It seems like compiling GMPECM with the withgwnum configuration option seems to (roughly) do the trick?

[QUOTE=mathwiz;510598]It seems like compiling GMPECM with the withgwnum configuration option seems to (roughly) do the trick?[/QUOTE]
Yes, but it may not work. As far as I know, no one has tried that for years. 
[QUOTE=Prime95;510609]Yes, but it may not work. As far as I know, no one has tried that for years.[/QUOTE]
Seems fine to me? Everything builds fine with the latest source... [code]GMPECM 7.0.4 [configured with GMP 6.1.2, GWNUM 29.4, enableasmredc] [ECM] Tuned for x86_64/k8/params.h Due to incompatible licenses, this binary file must not be distributed. Input number is (2^4096+1)/25860116183332395113497853167940236083358054650286886725246241569916604094012679963198712829716480001 (1133 digits) Found number: 1*2^4096 + 1 Using special division for factor of 2^4096+1 Using B1=850000000, B2=15892628251516, polynomial x^1, sigma=0:17241075805006320821 dF=524288, k=5, d=5705700, d2=17, i0=132 Expected number of curves to find a factor of n digits: 35 40 45 50 55 60 65 70 75 80 16 51 183 729 3188 15164 77841 427872 2503667 1.6e+07 Using gwnum_ecmStage1(1, 2, 4096, 1, 850000000, 1) Step 1 took 7762359ms Estimated memory usage: 13.58GB Initializing tables of differences for F took 3ms Computing roots of F took 11918ms Building F from its roots took 96743ms Computing 1/F took 80569ms Initializing table of differences for G took 140ms Computing roots of G took 8681ms Building G from its roots took 96779ms Computing roots of G took 8755ms Building G from its roots took 97078ms Computing G * H took 50789ms Reducing G * H mod F took 96635ms Computing roots of G took 9421ms Building G from its roots took 114522ms Computing G * H took 54272ms Reducing G * H mod F took 98293ms Computing roots of G took 8740ms Building G from its roots took 94358ms Computing G * H took 49260ms Reducing G * H mod F took 98047ms Computing roots of G took 8667ms Building G from its roots took 93193ms Computing G * H took 48465ms Reducing G * H mod F took 96023ms Computing polyeval(F,G) took 283192ms Computing product of all F(g_i) took 2667ms Step 2 took 1609858ms Expected time to find a factor of n digits: 35 40 45 50 55 60 65 70 75 80 1.78d 5.59d 19.89d 79.11d 345.78d 4.51y 23.13y 127.16y 744.07y 4613y[/code] 
Cool.
Can you test it to find known factors of F12? Maybe Xyzzy can dig up the sigma and bounds for his discovered factor. 
If this build finds known factors, I'm going to be finding some mersenne factors with it!
I wish you success, mathwiz. 
Here is the sigma from the F14 factor:
[url]https://mersenneforum.org/showpost.php?p=204429&postcount=18[/url] So you can test with: ecm.exe sigma 8585974330888598 110e6 110e8 < f14.txt where f14.txt is just "2^16384+1" 
After you've completed a QA run, be aware that stage 1 (I can't comment on stage 2) is not multithreaded. On a multicore machine you'll want to be running several instances during stage 1.
Stage 2 where access to memory is critical you'll probably only want one instance running  check with GMPECMers to see if this advice is accurate. 
[QUOTE=ATH;510639]Here is the sigma from the F14 factor:
[url]https://mersenneforum.org/showpost.php?p=204429&postcount=18[/url] So you can test with: ecm.exe sigma 8585974330888598 110e6 110e8 < f14.txt where f14.txt is just "2^16384+1"[/QUOTE] Yup. [code]Input number is 2^16384+1 (4933 digits) Found number: 1*2^16384 + 1 Using special division for factor of 2^16384+1 Using B1=110000000, B2=11000000000, polynomial x^1, sigma=0:8585974330888598 dF=16384, k=4, d=158340, d2=11, i0=684 Expected number of curves to find a factor of n digits: 35 40 45 50 55 60 65 70 75 80 73 308 1481 7942 46946 302925 2115419 1.6e+07 1.3e+08 1.1e+09 Using gwnum_ecmStage1(1, 2, 16384, 1, 110000000, 1) Step 1 took 3102146ms Estimated memory usage: 1.64GB Initializing tables of differences for F took 13ms Computing roots of F took 1634ms Building F from its roots took 3879ms Computing 1/F took 1515ms Initializing table of differences for G took 139ms Computing roots of G took 1282ms Building G from its roots took 3860ms Computing roots of G took 1282ms Building G from its roots took 3860ms Computing G * H took 844ms Reducing G * H mod F took 1269ms Computing roots of G took 1283ms Building G from its roots took 3853ms Computing G * H took 843ms Reducing G * H mod F took 1268ms Computing roots of G took 1282ms Building G from its roots took 3879ms Computing G * H took 846ms Reducing G * H mod F took 1270ms Computing polyeval(F,G) took 8930ms Computing product of all F(g_i) took 622ms Step 2 took 43778ms ********** Factor found in step 2: 116928085873074369829035993834596371340386703423373313 Found prime factor of 54 digits: 116928085873074369829035993834596371340386703423373313 Composite cofactor (2^16384+1)/116928085873074369829035993834596371340386703423373313 has 4880 digits Peak memory usage: 994MB[/code] 
Interestingly, GMPECM only seems to use gwnum_ecmStage1() if the input is written out explicitly in (2^n +/ 1)/d form, as opposed to a full decimal. E.g.:
[code]Input number is 7124875134919416452774071346240764917465050401053729788475829418006792633070197260773480462000925038600888030166963314178711084227927169505054967049906157236644045588489318562381444403587801123276191390920852492526599174604254696368010876509960456095578194840205874002033519141134093531142804832239163228700607998501023572045880402900991 (337 digits) Did not find a gwnum poly for the input number. Using special division for factor of 2^12431[/code] but [code]Input number is (2^12431)/(2^1131)/2047 (337 digits) Found number: 1*2^1243 + 1 Using special division for factor of 2^12431 Using B1=850000000, B2=15892628251516, polynomial Dickson(30), sigma=0:10702604903946832294 dF=524288, k=5, d=5705700, d2=17, i0=132 Expected number of curves to find a factor of n digits: 35 40 45 50 55 60 65 70 75 80 15 47 168 661 2867 13623 69471 381778 2221086 1.4e+07 Using gwnum_ecmStage1(1, 2, 1243, 1, 850000000, 1)[/code] 
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