From eea3eadf5b5b10249c77cdc0e351f5803bd6b68b Mon Sep 17 00:00:00 2001
From: Henry de Valence <hdevalence@hdevalence.ca>
Date: Thu, 14 Jun 2018 11:13:46 -0700
Subject: [PATCH] Replace special-case `swap_{AB,CD}` methods with general
 shuffles

---
 src/backend/avx2/edwards.rs |  7 +++----
 src/backend/avx2/field.rs   | 30 ++++--------------------------
 2 files changed, 7 insertions(+), 30 deletions(-)

diff --git a/src/backend/avx2/edwards.rs b/src/backend/avx2/edwards.rs
index a04c785..df446b7 100644
--- a/src/backend/avx2/edwards.rs
+++ b/src/backend/avx2/edwards.rs
@@ -177,9 +177,8 @@ impl<'a> Neg for &'a CachedPoint {
     type Output = CachedPoint;
 
     fn neg(self) -> CachedPoint {
-        let mut coords = self.0;
-        coords.swap_AB();
-        CachedPoint(coords.blend(coords.negate_lazy(), Lanes::D))
+        let swapped = self.0.shuffle(Shuffle::BACD);
+        CachedPoint(swapped.blend(swapped.negate_lazy(), Lanes::D))
     }
 }
 
@@ -197,7 +196,7 @@ impl<'a, 'b> Add<&'b CachedPoint> for &'a ExtendedPoint {
         tmp = &tmp * &other.0;
 
         // tmp = (S8 S9 S11 S10)
-        tmp.swap_CD();
+        tmp = tmp.shuffle(Shuffle::ABDC);
 
         // tmp = (S9-S8 S9+S8 S10-S11 S10+S11) = (S12 S13 S14 S15)
         tmp.diff_sum(Lanes::ABCD);
diff --git a/src/backend/avx2/field.rs b/src/backend/avx2/field.rs
index 082287d..ea6e6cb 100644
--- a/src/backend/avx2/field.rs
+++ b/src/backend/avx2/field.rs
@@ -106,6 +106,8 @@ pub enum Shuffle {
     CBCB,
     ABAB,
     BADC,
+    BACD,
+    ABDC,
 }
 
 /// A vector of four `FieldElements`, implemented using AVX2.
@@ -174,6 +176,8 @@ impl FieldElement32x4 {
                     Shuffle::CBCB => u32x8::new(4, 1, 6, 3, 4, 1, 6, 3),
                     Shuffle::ABAB => u32x8::new(0, 1, 2, 3, 0, 1, 2, 3),
                     Shuffle::BADC => u32x8::new(1, 0, 3, 2, 5, 4, 7, 6),
+                    Shuffle::BACD => u32x8::new(1, 0, 3, 2, 4, 5, 6, 7),
+                    Shuffle::ABDC => u32x8::new(0, 1, 2, 3, 5, 4, 7, 6),
                 };
                 // Note that this gets turned into a generic LLVM
                 // shuffle-by-constants, which can be lowered to a simpler
@@ -241,32 +245,6 @@ impl FieldElement32x4 {
         ])
     }
 
-    /// Given `self = (A,B,C,D)`, set `self = (B,A,C,D)`
-    pub fn swap_AB(&mut self) {
-        unsafe {
-            use core::arch::x86_64::_mm256_blend_epi32;
-            use core::arch::x86_64::_mm256_shuffle_epi32;
-            for i in 0..5 {
-                let swapped = _mm256_shuffle_epi32(self.0[i].into_bits(), 0b10_11_00_01);
-                self.0[i] =
-                    _mm256_blend_epi32(self.0[i].into_bits(), swapped, 0b00001111).into_bits();
-            }
-        }
-    }
-
-    /// Given `self = (A,B,C,D)`, set `self = (A,B,D,C)`
-    pub fn swap_CD(&mut self) {
-        unsafe {
-            use core::arch::x86_64::_mm256_blend_epi32;
-            use core::arch::x86_64::_mm256_shuffle_epi32;
-            for i in 0..5 {
-                let swapped = _mm256_shuffle_epi32(self.0[i].into_bits(), 0b10_11_00_01);
-                self.0[i] =
-                    _mm256_blend_epi32(self.0[i].into_bits(), swapped, 0b11110000).into_bits();
-            }
-        }
-    }
-
     /// Given `self = (A,B,C,D)`, set `self = (B - A, B + A, D - C, D + C)` according to `mask`.
     ///
     /// This is `#[inline(always)]` because the `mask` parameter should be an immediate.