add parallel g1/g2 msm gnark-crypto impl

[garyschulte]

Implement gnark MultiExp for g1/g2 MSM, using default degree of parallelism.

[siladu]

LGTM.

w.r.t the benchmark results, can you confirm

1. 24.9.1 is calling eip2537blsG1MultiExp
2. besu-gnark-single-parallel is calling eip2537blsG1MultiExpParallel but limiting to a single core (by setting nbTasks in the MultExpConfig?) This code isn't in this PR.
3. besu-gnark-parallel is calling eip2537blsG1MultiExpParallel using the implementation in this PR.

^ IIUC, then should we make (2) a configurable option, i.e. an option to limit to single core (not sure we need to expose a parameter for arbitrary cores?)

[garyschulte]

^ IIUC, then should we make (2) a configurable option, i.e. an option to limit to single core (not sure we need to expose a parameter for arbitrary cores?)

this seems like a reasonable idea. I think I can add the capability to configure NbTasks in the initialization of the gnark bls lib, and we can plumb an option in besu. I will 👀 at adding that bit of config and if it is as lightweight as I am thinking, will add it in this PR

Confirmed yes on 1, 2 and 3. re: # 2:

diff --git a/gnark/gnark-jni/gnark-eip-2537.go b/gnark/gnark-jni/gnark-eip-2537.go
index fdedf33..5217ee1 100644
--- a/gnark/gnark-jni/gnark-eip-2537.go
+++ b/gnark/gnark-jni/gnark-eip-2537.go
@@ -207,7 +207,7 @@ func eip2537blsG1MultiExpParallel(javaInputBuf, javaOutputBuf, javaErrorBuf *C.c
 
     var affineResult bls12381.G1Affine
     // leave nbTasks unset, allow golang to use available cpu cores as the parallelism limit
-    _, err := affineResult.MultiExp(g1Points, scalars, ecc.MultiExpConfig{})
+    _, err := affineResult.MultiExp(g1Points, scalars, ecc.MultiExpConfig{NbTasks: 1})
     if err != nil {
         copy(errorBuf, err.Error())
         return 1
@@ -377,7 +377,7 @@ func eip2537blsG2MultiExpParallel(javaInputBuf, javaOutputBuf, javaErrorBuf *C.c
 
     var affineResult bls12381.G2Affine
     // leave nbTasks unset, allow golang to use available cpu cores as the parallelism limit
-    _, err := affineResult.MultiExp(g2Points, scalars, ecc.MultiExpConfig{})
+    _, err := affineResult.MultiExp(g2Points, scalars, ecc.MultiExpConfig{NbTasks: 1})
     if err != nil {
         copy(errorBuf, err.Error())
         return 1
@@ -387,10 +387,6 @@ func eip2537blsG2MultiExpParallel(javaInputBuf, javaOutputBuf, javaErrorBuf *C.c
     return nonMontgomeryMarshalG2(&affineResult, javaOutputBuf, errorBuf)
 }