From 7ffeba3ae46ac777d8d4f91ca1c94a42d848aa98 Mon Sep 17 00:00:00 2001
From: Daniel Lubarov <daniel@lubarov.com>
Date: Sun, 12 Sep 2021 18:29:07 -0700
Subject: [PATCH] Delete my old MDS code, now obsolete

---
 src/field/crandall_field.rs | 95 -------------------------------------
 src/field/field_types.rs    | 29 -----------
 2 files changed, 124 deletions(-)

diff --git a/src/field/crandall_field.rs b/src/field/crandall_field.rs
index 7688bf81..d2227d80 100644
--- a/src/field/crandall_field.rs
+++ b/src/field/crandall_field.rs
@@ -17,90 +17,6 @@ use crate::field::inversion::try_inverse_u64;
 /// EPSILON = 9 * 2**28 - 1
 const EPSILON: u64 = 2415919103;
 
-/// A precomputed 8*8 Cauchy matrix, generated with `Field::mds_8`.
-const CAUCHY_MDS_8: [[CrandallField; 8]; 8] = [
-    [
-        CrandallField(16140901062381928449),
-        CrandallField(2635249153041947502),
-        CrandallField(3074457345215605419),
-        CrandallField(11068046442776179508),
-        CrandallField(13835058053470224385),
-        CrandallField(6148914690431210838),
-        CrandallField(9223372035646816257),
-        CrandallField(1),
-    ],
-    [
-        CrandallField(2049638230143736946),
-        CrandallField(16140901062381928449),
-        CrandallField(2635249153041947502),
-        CrandallField(3074457345215605419),
-        CrandallField(11068046442776179508),
-        CrandallField(13835058053470224385),
-        CrandallField(6148914690431210838),
-        CrandallField(9223372035646816257),
-    ],
-    [
-        CrandallField(5534023221388089754),
-        CrandallField(2049638230143736946),
-        CrandallField(16140901062381928449),
-        CrandallField(2635249153041947502),
-        CrandallField(3074457345215605419),
-        CrandallField(11068046442776179508),
-        CrandallField(13835058053470224385),
-        CrandallField(6148914690431210838),
-    ],
-    [
-        CrandallField(16769767337539665921),
-        CrandallField(5534023221388089754),
-        CrandallField(2049638230143736946),
-        CrandallField(16140901062381928449),
-        CrandallField(2635249153041947502),
-        CrandallField(3074457345215605419),
-        CrandallField(11068046442776179508),
-        CrandallField(13835058053470224385),
-    ],
-    [
-        CrandallField(10760600708254618966),
-        CrandallField(16769767337539665921),
-        CrandallField(5534023221388089754),
-        CrandallField(2049638230143736946),
-        CrandallField(16140901062381928449),
-        CrandallField(2635249153041947502),
-        CrandallField(3074457345215605419),
-        CrandallField(11068046442776179508),
-    ],
-    [
-        CrandallField(5675921252705733081),
-        CrandallField(10760600708254618966),
-        CrandallField(16769767337539665921),
-        CrandallField(5534023221388089754),
-        CrandallField(2049638230143736946),
-        CrandallField(16140901062381928449),
-        CrandallField(2635249153041947502),
-        CrandallField(3074457345215605419),
-    ],
-    [
-        CrandallField(1317624576520973751),
-        CrandallField(5675921252705733081),
-        CrandallField(10760600708254618966),
-        CrandallField(16769767337539665921),
-        CrandallField(5534023221388089754),
-        CrandallField(2049638230143736946),
-        CrandallField(16140901062381928449),
-        CrandallField(2635249153041947502),
-    ],
-    [
-        CrandallField(15987178195121148178),
-        CrandallField(1317624576520973751),
-        CrandallField(5675921252705733081),
-        CrandallField(10760600708254618966),
-        CrandallField(16769767337539665921),
-        CrandallField(5534023221388089754),
-        CrandallField(2049638230143736946),
-        CrandallField(16140901062381928449),
-    ],
-];
-
 /// A field designed for use with the Crandall reduction algorithm.
 ///
 /// Its order is
@@ -257,17 +173,6 @@ impl Field for CrandallField {
         let x74 = x73 * x39;
         x74
     }
-
-    fn mds_8(vec: [Self; 8]) -> [Self; 8] {
-        let mut result = [Self::ZERO; 8];
-        for r in 0..8 {
-            for c in 0..8 {
-                let entry = CAUCHY_MDS_8[r][c];
-                result[r] += entry * vec[c];
-            }
-        }
-        result
-    }
 }
 
 impl PrimeField for CrandallField {
diff --git a/src/field/field_types.rs b/src/field/field_types.rs
index 62313826..0038dec7 100644
--- a/src/field/field_types.rs
+++ b/src/field/field_types.rs
@@ -280,35 +280,6 @@ pub trait Field:
         }
     }
 
-    /// Apply an MDS matrix to the given vector. Any MDS matrix can be used, as long as the same one
-    /// is used among calls with the same vector length.
-    ///
-    /// Note that the default implementation is quite slow. If speed is important, this should be
-    /// overridden with a field-specific implementation which applies a precomputed MDS matrix.
-    fn mds(vec: Vec<Self>) -> Vec<Self> {
-        // We use a Cauchy matrix with x_r = n + r, y_c = c.
-        let n = vec.len();
-        let mut result = Vec::with_capacity(n);
-        for r in 0..n {
-            let mut sum = Self::ZERO;
-            for c in 0..n {
-                let x = Self::from_canonical_usize(n + r);
-                let y = Self::from_canonical_usize(c);
-                // This is the (r, c) entry of the Cauchy matrix.
-                let entry = (x - y).inverse();
-                sum += entry * vec[c];
-            }
-            result.push(sum);
-        }
-        result
-    }
-
-    /// Like `mds`, but specialized to n=8. For specific fields, this can be overridden with an
-    /// impl which applies a fast, precomputed 8x8 MDS matrix.
-    fn mds_8(vec: [Self; 8]) -> [Self; 8] {
-        Self::mds(vec.to_vec()).try_into().unwrap()
-    }
-
     fn rand() -> Self {
         Self::rand_from_rng(&mut rand::thread_rng())
     }