Gas estimation
FHE operations are typically more computationally expensive than classical operations due to their inherent complexity. As a reference, here is an approximation of the gas cost associated with each operation.
ebool
and
/or
/xor
26,000
not
30,000
decrypt
500,000
euint4
add
/sub
65,000
add
/sub
(scalar)
65,000
mul
150,000
mul
(scalar)
88,000
div
(scalar)
139,000
rem
(scalar)
286,000
and
/or
/xor
32,000
shr
/shl
116,000
shr
/shl
(scalar)
35,000
rotr
/rotl
116,000
rotr
/rotl
(scalar)
35,000
eq
/ne
51,000
ge
/gt
/le
/lt
70,000
min
/max
121,000
min
/max
(scalar)
121,000
neg
60,000
not
33,000
select
45,000
decrypt
500,000
euint8
add
/sub
94,000
add
/sub
(scalar)
94,000
mul
197,000
mul
(scalar)
159,000
div
(scalar)
238,000
rem
(scalar)
460,000
and
/or
/xor
34,000
shr
/shl
133,000
shr
/shl
(scalar)
35,000
rotr
/rotl
133,000
rotr
/rotl
(scalar)
35,000
eq
/ne
53,000
ge
/gt
/le
/lt
82,000
min
/max
128,000
min
/max
(scalar)
128,000
neg
95,000
not
34,000
select
47,000
decrypt
500,000
randEuint8()
100,000
euint16
add
/sub
133,000
add
/sub
(scalar)
133,000
mul
262,000
mul
(scalar)
208,000
div
(scalar)
314,000
rem
(scalar)
622,000
and
/or
/xor
34,000
shr
/shl
153,000
shr
/shl
(scalar)
35,000
rotr
/rotl
153,000
rotr
/rotl
(scalar)
35,000
eq
/ne
54,000
ge
/gt
/le
/lt
105,000
min
/max
153,000
min
/max
(scalar)
150,000
neg
131,000
not
35,000
select
47,000
decrypt
500,000
randEuint16()
100,000
euint32
add
/sub
162,000
add
/sub
(scalar)
162,000
mul
359,000
mul
(scalar)
264,000
div
(scalar)
398,000
rem
(scalar)
805,000
and
/or
/xor
35,000
shr
/shl
183,000
shr
/shl
(scalar)
35,000
rotr
/rotl
183,000
rotr
/rotl
(scalar)
35,000
eq
/ne
82,000
ge
/gt
/le
/lt
128,000
min
/max
183,000
min
/max
(scalar)
164,000
neg
160,000
not
36,000
select
50,000
decrypt
500,000
randEuint32()
100,000
euint64
add
/sub
188,000
add
/sub
(scalar)
188,000
mul
641,000
mul
(scalar)
356,000
div
(scalar)
584,000
rem
(scalar)
1,095,000
and
/or
/xor
38,000
shr
/shl
227,000
shr
/shl
(scalar)
38,000
rotr
/rotl
227,000
rotr
/rotl
(scalar)
38,000
eq
/ne
86,000
ge
/gt
/le
/lt
156,000
min
/max
210,000
min
/max
(scalar)
192,000
neg
199,000
not
37,000
select
53,000
decrypt
500,000
randEuint64()
100,000
eaddress
eq
/ne
90,000
Estimate gas
When you call estimate gas method, we can’t determine accurately the gas usage if your function uses TFHE.decrypt
. During gas estimation, all TFHE.decrypt()
will return 1
.
What does it mean?
require(TFHE.decrypt(ebool));
will be ok butrequire(!TFHE.decrypt(ebool));
will fail during estimation (revert transaction)A loop, where you expect a decrypt to be false to break, will never end in gas estimate method (and fails), since the decrypt will always return
1
(true)On the other hand, if your loop should last 2 or 3 cycles, until the value is 1, the estimation will be below.
If you have branches (if/else) based on a decryption, the estimation will use the branch running when the decryption is
1
While it’s challenging to accurately estimate gas consumption when using TFHE.decrypt
, we strongly encourage you to take this into consideration.
What can I do?
A possible solution is to overestimate your gas estimation. You can take this function (with ethers.js) as an example where we multiply the gas limit by 1.2
.
Gas limit
The current devnet has a gas limit of 10,000,000. If you send a transaction exceeding this limit, it won't be executed. Consequently, your wallet won't be able to emit a new transaction. To address this, emit a new transaction with the same nonce but the correct gas limit. In Metamask, you can enforce the use of a specific nonce by enabling the feature in 'Advanced Settings'.
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