From 447bee57eed2d9c9cfe80532f5ffe98179a360d1 Mon Sep 17 00:00:00 2001
From: supinie <86788874+supinie@users.noreply.github.com>
Date: Mon, 27 May 2024 16:57:52 +0100
Subject: [PATCH] add explanation for new consts

---
 src/params.rs      |  8 ++++++--
 src/polynomials.rs | 15 +++++++++------
 src/vectors.rs     | 10 +++++++---
 3 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/src/params.rs b/src/params.rs
index 82054aa..5a7f72d 100644
--- a/src/params.rs
+++ b/src/params.rs
@@ -4,13 +4,17 @@ use num_enum::{IntoPrimitive, TryFromPrimitive};
 pub const N: usize = 256;
 
 pub const Q: usize = 3329;
+#[allow(clippy::cast_possible_truncation, clippy::cast_possible_wrap)]
 pub const Q_I16: i16 = Q as i16;
+#[allow(clippy::cast_possible_truncation, clippy::cast_possible_wrap)]
 pub const Q_U16: u16 = Q as u16;
+#[allow(clippy::cast_possible_truncation, clippy::cast_possible_wrap)]
 pub const Q_I32: i32 = Q as i32;
+#[allow(clippy::cast_possible_truncation, clippy::cast_possible_wrap)]
 pub const Q_U32: u32 = Q as u32;
 
-pub const Q_DIV: u64 = 80635;
-pub const Q_DIV_VEC: u64 = 1290167;
+pub const Q_DIV: u64 = 80_635; // round(2^28 / Q)
+pub const Q_DIV_VEC: u64 = 1_290_167; // round(2^32 / Q)
 
 pub const SYMBYTES: usize = 32; // size of hashes
 
diff --git a/src/polynomials.rs b/src/polynomials.rs
index 9494280..9b37380 100644
--- a/src/polynomials.rs
+++ b/src/polynomials.rs
@@ -4,7 +4,7 @@ mod sample;
 use crate::{
     errors::{CrystalsError, PackingError},
     field_operations::{barrett_reduce, conditional_sub_q, mont_form, montgomery_reduce},
-    params::{SecurityLevel, N, POLYBYTES, Q, Q_I16, Q_U16, Q_U32, Q_DIV, SYMBYTES},
+    params::{SecurityLevel, N, POLYBYTES, Q, Q_DIV, Q_I16, Q_U16, Q_U32, SYMBYTES},
     polynomials::ntt::ZETAS,
 };
 use core::num::TryFromIntError;
@@ -319,7 +319,9 @@ impl Poly<Normalised> {
                         let mut temp = *coeff;
                         temp += (temp >> 15) & Q_I16;
                         *t_elem = u8::try_from(
-                            (((((u64::try_from(temp)?) << 4) + u64::from(Q_U16 / 2)) * Q_DIV) >> 28) & 0xf,
+                            (((((u64::try_from(temp)?) << 4) + u64::from(Q_U16 / 2)) * Q_DIV)
+                                >> 28)
+                                & 0xf,
                         )?;
                     }
 
@@ -340,7 +342,10 @@ impl Poly<Normalised> {
                         let mut temp = *coeff;
                         temp += (temp >> 15) & Q_I16;
                         *t_elem = u8::try_from(
-                            (((((u64::try_from(temp)?) << 5) + u64::from(Q_U32 / 2)) * (Q_DIV / 2)) >> 27) & 0x1f,
+                            (((((u64::try_from(temp)?) << 5) + u64::from(Q_U32 / 2))
+                                * (Q_DIV / 2))
+                                >> 27)
+                                & 0x1f,
                         )?;
                     }
 
@@ -467,9 +472,7 @@ impl Poly<Normalised> {
                         buf_chunk[4] >> 3,
                     ];
                     for (coeff, t_elem) in coeffs_chunk.iter_mut().zip(temp.iter()) {
-                        *coeff = i16::try_from(
-                            ((u32::from(*t_elem) & 31) * Q_U32 + 16) >> 5,
-                        )?;
+                        *coeff = i16::try_from(((u32::from(*t_elem) & 31) * Q_U32 + 16) >> 5)?;
                     }
                 }
                 Ok(Self {
diff --git a/src/vectors.rs b/src/vectors.rs
index 722f270..024f89b 100644
--- a/src/vectors.rs
+++ b/src/vectors.rs
@@ -1,6 +1,6 @@
 use crate::{
     errors::{CrystalsError, PackingError},
-    params::{Eta, SecurityLevel, K, N, POLYBYTES, Q_I16, Q_U32, Q_DIV_VEC},
+    params::{Eta, SecurityLevel, K, N, POLYBYTES, Q_DIV_VEC, Q_I16, Q_U32},
     polynomials::{Barrett, Montgomery, Normalised, Poly, Reduced, State, Unnormalised, Unreduced},
 };
 use tinyvec::{array_vec, ArrayVec};
@@ -184,7 +184,9 @@ impl PolyVec<Normalised> {
                             *t_elem = *coeff as u16;
                             *t_elem =
                                 t_elem.wrapping_add((((*t_elem as i16) >> 15) & Q_I16) as u16);
-                            *t_elem = (((((u64::from(*t_elem) << 10) + u64::from(Q_U32 / 2)) * Q_DIV_VEC) >> 32)
+                            *t_elem = (((((u64::from(*t_elem) << 10) + u64::from(Q_U32 / 2))
+                                * Q_DIV_VEC)
+                                >> 32)
                                 & 0x3ff) as u16;
                         }
 
@@ -225,7 +227,9 @@ impl PolyVec<Normalised> {
                             *t_elem = *coeff as u16;
                             *t_elem =
                                 t_elem.wrapping_add((((*t_elem as i16) >> 15) & Q_I16) as u16);
-                            *t_elem = (((((u64::from(*t_elem) << 11) + u64::from(Q_U32 / 2)) * (Q_DIV_VEC / 2)) >> 31)
+                            *t_elem = (((((u64::from(*t_elem) << 11) + u64::from(Q_U32 / 2))
+                                * (Q_DIV_VEC / 2))
+                                >> 31)
                                 & 0x7ff) as u16;
                         }