Poseidon2 permutation seems to work

.gitignore

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+.DS_Store
+Cargo.lock
+/target
+/tmp

Cargo.toml

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+[package]
+name    = "rust-poseidon2-bn254"
+version = "0.0.0"
+edition = "2021"
+license = "MIT OR Apache-2.0"
+
+[dependencies]
+lazy_static = { version = "1.5.0" }
+ark-std     = { version = "0.5.0" }
+ark-ff      = { version = "0.5.0" }
+ark-bn254   = { version = "0.5.0" }

README.md

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+
+`rust-poseidon2-bn254`
+--------------------
+
+Rust implementation of the Poseidon2 hash function over the BN254 curve's scalar field
+(with `t=3`). 
+
+Currently using [arkworks](https://github.com/arkworks-rs) for field arithmetic.
+

src/constants.rs

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+
+use lazy_static::lazy_static;
+
+use ark_std::str::FromStr;
+use ark_bn254::Fr as F;
+
+//------------------------------------------------------------------------------
+
+fn unsafe_field_from_str(x: &str) -> F {
+  F::from_str(x).unwrap()
+}
+
+//------------------------------------------------------------------------------
+
+lazy_static! {
+  pub static ref EXTERNAL_ROUND_CONST: [F; 24] =
+    EXTERNAL_ROUND_CONST_STR.into_iter().map( unsafe_field_from_str ).collect::<Vec<F>>().try_into().unwrap();
+}
+
+lazy_static! {
+  pub static ref INTERNAL_ROUND_CONST: [F; 56] =
+    INTERNAL_ROUND_CONST_STR.into_iter().map( unsafe_field_from_str ).collect::<Vec<F>>().try_into().unwrap();
+}
+
+//------------------------------------------------------------------------------
+
+static EXTERNAL_ROUND_CONST_STR: [&str; 24] =
+  [ "20036611579827150559091469005844175073625940102952070649817884191797764107075"
+  , "12833584042949159986565784794014151972247796182705941809242049488642050965764"
+  , "20460265239335923814507658708649753625122635556480788121847315929099732630160"
+  , "2327433556176440050072122789158937095349015830966296688052004527413893088211"
+  , "18928950063089170035907725405866336756839578021518946851617532132424258251714"
+  , "1498343560697108822498273562774300261830404487630763796790963549875888044170"
+  , "10894060797649430325830102265601652830696874259935838091685396334824506870974"
+  , "10724282231429846920698162462239380161919181405938370346044877808218935812722"
+  , "12900822782410361357346122719301635014682733276151991957222022994303272655598"
+  , "12281187892168564254318627327513968787860396596558174241050192282039059721015"
+  , "20650821582781615100585145227212437582142977940055542470636589623435638972974"
+  , "10629768372315475914205126397268924392851627409938344639024631693382468091238"
+  , "16917851076945834679745654051495359311013500015444379399867812928847812812510"
+  , "5864181025763406655115777223889072827293022750325008731169039770623910915277"
+  , "10954281474369541712624748628862576225398375445664590376470032986861704444851"
+  , "13047511983320021446527738191176357616721874803157974120155396052149484216634"
+  , "17384764166393886603954067639141617082485023441458666471633998399316404519396"
+  , "2362259915869885612166233838782699563177506073802792748904427749547307239091"
+  , "3449611877995076637446149781868130604254776727586032907573864421212958534148"
+  , "8105036071757751706553034047983212897131570345551297243248892142702129409678"
+  , "4057622885794382454162574102227879765926272192471614700281108386186208378108"
+  , "19253655284986776930766796883935217167812408888646382124396693895764793065618"
+  , "14562077372515720927783340475811850803822078325552042696568002577429594161808"
+  , "7014243471382661219949882659461009076113783570411660059539677464905457050066"
+  ];
+
+//------------------------------------------------------------------------------
+
+static INTERNAL_ROUND_CONST_STR: [&str; 56] =
+  [ "9863412385841952362091849999302344670551536862597895561278739824943955436428"
+  , "12647165719356049717276082841324782064533712829755618494899697790036659206896"
+  , "7086910375195160419007414095698529055230556352178368086440281946317648386880"
+  , "3534616497502400285225524656623573157846352519939301302938694874082052072531"
+  , "7614193770971378304733014379518957809467088529876055633743098033063991937988"
+  , "5524517084220026554140171636731805466222414790303448093874175843707842149296"
+  , "6465594825680448812389988135904471523354179427789234651961801931723687100590"
+  , "13069961729933398081974430219710353490873542026760226429212509555519019152029"
+  , "20442858075434477469830277030056901344749316967720547608602986649544991223254"
+  , "2545061208850080799716748664877827143438576541109233212439269028123126995283"
+  , "10590804083025333327978466704873260869373451484886744716135293454855421776182"
+  , "2971801848580094041349173303826341900320100639936132696391170461147651791599"
+  , "6457488363353205666653234338157121013068090150457850441006724736538329117150"
+  , "6828448758803946230526683011338306528814963654399318058641145666219257935090"
+  , "21220571338383411884578252416062534137998565615530587243864120751033430171639"
+  , "3026330605417380631686907051427895875297995068925155493166857059368062462182"
+  , "731369258216230615295136666016875570919026708063642185179381726677850241678"
+  , "3976056293038938116541801753309319302894026070844887224129384450572018141696"
+  , "18191771098193274629372635247562817907522214770330118615218435763543549998849"
+  , "5725653743840821273222706240430501486301231493172435748281584336969930288424"
+  , "11315632284569557454743403424858271195359234409995993988812038704370836780935"
+  , "1554548474507260015710470936845569353450016357484523407182389210520378329681"
+  , "4043703307392904605083268263455220115794158610223459176828550627728253474746"
+  , "5147341731800747507000152527876279909425699775431448328748957228886538246347"
+  , "316000240737142429159443531715814797123772606639483557601339985787766020188"
+  , "9201639581870600108429525788569689133841787929111628476773761218482387877013"
+  , "76452313668236664875560655448227033496493983051536430171258861062052191226"
+  , "5503629712269636063700501314848921574392241749467380315893984871270736181455"
+  , "6403315002483104841708481320831358853734637389275574672824410469941470947501"
+  , "18767770632814906108167838116228345063195454403262264488888241387554264238660"
+  , "373847975877840160326133445669241099117560443926620032996032499044947786206"
+  , "21583421457099893419202355352294471270616995660291443431182584120442735921995"
+  , "9983253793391637270425117523681631923584433357117997691348261314215409417977"
+  , "15636580057941931488663342701921482616732902735747145545560675417041959528168"
+  , "13987037342707768451704041319080865947736730484739494822133564732867708182129"
+  , "17012807810939334924306150791435050869173026502739324471672493058506335677602"
+  , "20445006141370558272839096434547759512337597485395700957462476332341263470795"
+  , "8919512276260973838722894975323643726180891487427800112399328013257265098884"
+  , "5121935724947519798577565968119435009768355186616305612599005246528173860072"
+  , "14390107556389236497954661819339690487046314759239155128415464040636056995180"
+  , "15584006578697113728990467783042934569634784959449117771168091586065677667289"
+  , "1894113083403807703900670244801865115743187370284525340414788037116278755190"
+  , "10705487296676443016268478693800719585977460625398657826409495078078625785779"
+  , "19873128801331021326057263165428495080386730321288221112754217581989746046187"
+  , "9535868612309525085410638759100096355215966759273780340615254181304597180876"
+  , "19343524237095964073059512688602276354221693507832098135091590955813103860375"
+  , "6822002759027581661397720296774923367218318024525870595858692787302610345838"
+  , "20926315677022871764300366782923548421637739455364254388830334528197327379743"
+  , "21136323309320513006223521228388165385265667945268848018308200096388016784087"
+  , "6225919113652258029432904641421409709120407088870082365870799895213524311811"
+  , "21311480157558702908741067111471547471593313246226635294078364811203226453373"
+  , "14198190262525448445981718442399104668575545443532459171696901751739593839857"
+  , "12459931960399741184291910088669153631848894479486118281597822681015713751918"
+  , "6907332911214986094624912982222847460679912779076715919016253686198271600395"
+  , "3393759605179403680839415959192212038674751416897927769901727596993250674985"
+  , "16080342864802322672358399934807873723002376453489101187414456500323890285012"
+  ];
+
+//------------------------------------------------------------------------------

src/lib.rs

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+mod constants;
+pub mod poseidon2;

src/poseidon2.rs

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+
+//use ark_ff::{Field,PrimeField};
+use ark_bn254::Fr as F;
+
+use crate::constants::*;
+
+//------------------------------------------------------------------------------
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)] 
+pub struct State { x: F, y: F, z: F } 
+
+//------------------------------------------------------------------------------
+
+fn sbox(x: F) -> F {
+  let x2: F = x * x;
+  let x4: F = x2*x2;
+  x*x4
+}
+
+fn linear_layer(u: &mut State) {
+  let s = u.x + u.y + u.z;
+  u.x += s;
+  u.y += s;
+  u.z += s;
+}
+
+//------------------------------------------------------------------------------
+
+fn internal_round(j: usize, u: &mut State) {
+  let x1 = sbox( u.x + INTERNAL_ROUND_CONST[j] );
+  let s  = x1 + u.y + u.z;
+  u.x = s + x1 ;
+  u.y = s + u.y;
+  u.z = s + u.z + u.z;
+}
+
+fn external_round(j: usize, u: &mut State) {
+  let k  = 3*j;
+  let x1 = sbox( u.x + EXTERNAL_ROUND_CONST[k+0] );
+  let y1 = sbox( u.y + EXTERNAL_ROUND_CONST[k+1] );
+  let z1 = sbox( u.z + EXTERNAL_ROUND_CONST[k+2] );
+  let s  = x1 + y1 + z1;
+  u.x = s + x1;
+  u.y = s + y1;
+  u.z = s + z1;
+}
+
+//------------------------------------------------------------------------------
+
+pub fn permute_inplace(u: &mut State) {
+  linear_layer(u);
+  for j in 0..4  { external_round(j, u); }
+  for j in 0..56 { internal_round(j, u); }
+  for j in 4..8  { external_round(j, u); }
+}
+
+pub fn permute(u: State) -> State {
+  let mut v = u;
+  permute_inplace(&mut v);
+  v
+}
+
+//------------------------------------------------------------------------------
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+  use ark_std::str::FromStr;
+
+  #[test]
+  fn permute_kat() {
+    let input    = State { x: F::from(0u64), y: F::from(1u64), z: F::from(2u64) };
+    let output   = permute(input);
+    println!("x = {}",output.x);
+    println!("y = {}",output.y);
+    println!("z = {}",output.z);
+    let expected = State 
+          { x: F::from_str("21882471761025344482456282050943515707267606647948403374880378562101343146243").unwrap()
+          , y: F::from_str("9030699330013392132529464674294378792132780497765201297316864012141442630280" ).unwrap()
+          , z: F::from_str("9137931384593657624554037900714196568304064431583163402259937475584578975855" ).unwrap()
+          };
+    assert_eq!(output,expected);
+  }
+}