Circuit breaks down on some inputs. #921

infinite-pursuits · 2023-11-17T07:32:05Z

infinite-pursuits
Nov 17, 2023

Hi, I have the following circuit.

type verifyprojection struct {
	Ca              [inputsizeconst]frontend.Variable     `gnark:"a"`
	Ca_abs          [inputsizeconst - 1]frontend.Variable `gnark:"a_abs"`
	Cb_extra_scaled frontend.Variable                     `gnark:"b_extra_scaled"`
	Cx0             [inputsizeconst]frontend.Variable     `gnark:"x0"`
	Cprojsq         frontend.Variable                     `gnark:"Cprojsq"`
	Limitsq_eq frontend.Variable `gnark:"Limit"`
}

func (circuit *verifyprojection) Define(api frontend.API) error {
	ax := dotpdtf(api, circuit.Ca, circuit.Cx0)
	num := api.Sub(circuit.Cb_extra_scaled, ax)
	numsq := api.Mul(num, num)
	denom := dotpdtfsmallsize(api, circuit.Ca_abs, circuit.Ca_abs) 
	lhs_sq := api.Mul(circuit.Cprojsq, denom)

	fieldsize := api.Compiler().Field()
	fieldsize_minusone := api.Sub(fieldsize, frontend.Variable(1))
	field_mid := api.Div(fieldsize_minusone, frontend.Variable(2))
	upperlimit := api.Add(field_mid, circuit.Limitsq_eq)
	lowerlimit := api.Sub(field_mid, circuit.Limitsq_eq)

	val := api.Sub(lhs_sq, numsq)
	val = api.Add(val, field_mid)

	api.AssertIsLessOrEqual(lowerlimit, val)
	api.AssertIsLessOrEqual(val, upperlimit)

	return nil
}

This circuit works mostly, but breaks down sometimes in the groth16.Prove step, giving the error - panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x50 pc=0x13ef331]

Can someone please guide me to why this error could be occuring?

This circuit works for the following inputs:

Ca:  &{{14 [-749 7595 4643 -7458 -52355 27021 -21436 28547 -21047 23253 -5280 9439 -12540 -3037] 1}}
Ca_abs:  &{{13 [7595 4643 7458 52355 27021 21436 28547 21047 23253 5280 9439 12540 3037] 1}}
Cb_extra_scaled: -26484000
Cx0: [1000 -647 -213 506 180 -438 -390 -738 -884 384 -147 -219 -78 263]
Cprojsq:  11793
Limitsq_eq: 1000000000000

But it breaks down for the following input:

Ca:  &{{14 [43442 -440510 -269294 432564 3.03659e+06 -1.567218e+06 1.243288e+06 -1.655726e+06 1.220726e+06 -1.348674e+06 306240 -547462 727320 176146] 1}}
Ca_abs:  &{{13 [440510 269294 432564 3.03659e+06 1.567218e+06 1.243288e+06 1.655726e+06 1.220726e+06 1.348674e+06 306240 547462 727320 176146] 1}}
Cb_extra_scaled: 1537084000
Cx0: [1000 -647 -213 506 180 -438 -390 -738 -884 384 -147 -219 -78 263]
Cprojsq:  11842
Limitsq_eq: 1000000000000

The dotpdtf and dotpdtfsmallsize functions are as defined:

func dotpdtf(api frontend.API, v1 [inputsizeconst]frontend.Variable, v2 [inputsizeconst]frontend.Variable) frontend.Variable {
	var tempsum frontend.Variable
	tempsum = 0
	l := len(v1)
	for i := 0; i < l; i++ {
		a := api.Mul(v1[i], v2[i])
		tempsum = api.Add(a, tempsum)
]	}
	return tempsum
}

func dotpdtfsmallsize(api frontend.API, v1 [inputsizeconst - 1]frontend.Variable, v2 [inputsizeconst - 1]frontend.Variable) frontend.Variable {
	var tempsum frontend.Variable
	tempsum = 0
	l := len(v1)
	for i := 0; i < l; i++ {
		a := api.Mul(v1[i], v2[i])
		tempsum = api.Add(a, tempsum)
	}
	return tempsum
}