From 5841bf9f3d3cfd2123c9340d4a0f00aa805f61c5 Mon Sep 17 00:00:00 2001
From: Thomas Lively <tlively@google.com>
Date: Thu, 12 Sep 2019 18:25:29 -0700
Subject: [PATCH 1/3] Add pseudocode for widening and narrowing operations

Clarifies that high lanes are lanes `[0, n/2)` and low lanes are
`[n/2, n)` and that the order of arguments to the narrowing ops
are (low, high). This matches the current implementation in V8.
---
 proposals/simd/SIMD.md | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/proposals/simd/SIMD.md b/proposals/simd/SIMD.md
index 4f9e073f6..980ef00ed 100644
--- a/proposals/simd/SIMD.md
+++ b/proposals/simd/SIMD.md
@@ -808,6 +808,28 @@ will use unsigned saturation to handle overflow, 0x00 or 0xff for i8x16.
 Regardless of the whether the operation is signed or unsigned, the input lanes
 are interpreted as signed integers.
 
+```python
+def S.narrow_T_s(a, b):
+    result = S.New()
+    for i in range(T.Lanes):
+        result[i] = S.SignedSaturate(b[i])
+    for i in range(T.Lanes):
+        result[T.Lanes + i] = S.SignedSaturate(a[i])
+    return result
+
+```
+
+```python
+def S.narrow_T_u(a, b):
+    result = S.New()
+    for i in range(T.Lanes):
+        result[i] = S.UnsignedSaturate(b[i])
+    for i in range(T.Lanes):
+        result[T.Lanes + i] = S.UnsignedSaturate(a[i])
+    return result
+
+```
+
 ### Integer to integer widening
 * `i16x8.widen_low_i8x16_s(a: v128) -> v128`
 * `i16x8.widen_high_i8x16_s(a: v128) -> v128`
@@ -820,3 +842,21 @@ are interpreted as signed integers.
 
 Converts low or high half of the smaller lane vector to a larger lane vector,
 sign extended or zero (unsigned) extended.
+
+```python
+def S.widen_low_T(ext, a):
+    result = S.New()
+    for i in range(S.Lanes):
+        result[i] = ext(a[S.Lanes + i])
+
+def S.widen_high_T(ext, a):
+    result = S.New()
+    for i in range(S.Lanes):
+        result[i] = ext(a[i])
+
+def S.widen_low_T_s(a):
+    return S.widen_low_T(Sext, a)
+
+def S.widen_high_T_u(a):
+    return S.widen_high_T(Zext, a)
+```

From e68d2141a7b2785ace98721733f85a7cf45289b2 Mon Sep 17 00:00:00 2001
From: Thomas Lively <tlively@google.com>
Date: Fri, 13 Sep 2019 11:19:20 -0700
Subject: [PATCH 2/3] Switch to "low" meaning [0,n/2) and "high" meaning
 [n/2,n)

---
 proposals/simd/SIMD.md | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/proposals/simd/SIMD.md b/proposals/simd/SIMD.md
index 980ef00ed..ca45131e5 100644
--- a/proposals/simd/SIMD.md
+++ b/proposals/simd/SIMD.md
@@ -812,9 +812,9 @@ are interpreted as signed integers.
 def S.narrow_T_s(a, b):
     result = S.New()
     for i in range(T.Lanes):
-        result[i] = S.SignedSaturate(b[i])
+        result[i] = S.SignedSaturate(a[i])
     for i in range(T.Lanes):
-        result[T.Lanes + i] = S.SignedSaturate(a[i])
+        result[T.Lanes + i] = S.SignedSaturate(b[i])
     return result
 
 ```
@@ -823,9 +823,9 @@ def S.narrow_T_s(a, b):
 def S.narrow_T_u(a, b):
     result = S.New()
     for i in range(T.Lanes):
-        result[i] = S.UnsignedSaturate(b[i])
+        result[i] = S.UnsignedSaturate(a[i])
     for i in range(T.Lanes):
-        result[T.Lanes + i] = S.UnsignedSaturate(a[i])
+        result[T.Lanes + i] = S.UnsignedSaturate(b[i])
     return result
 
 ```
@@ -847,16 +847,22 @@ sign extended or zero (unsigned) extended.
 def S.widen_low_T(ext, a):
     result = S.New()
     for i in range(S.Lanes):
-        result[i] = ext(a[S.Lanes + i])
+        result[i] = ext(a[i])
 
 def S.widen_high_T(ext, a):
     result = S.New()
     for i in range(S.Lanes):
-        result[i] = ext(a[i])
+        result[i] = ext(a[S.Lanes + i])
 
 def S.widen_low_T_s(a):
     return S.widen_low_T(Sext, a)
 
+def S.widen_high_T_s(a):
+    return S.widen_high_T(Sext, a)
+
+def S.widen_low_T_u(a):
+    return S.widen_low_T(Zext, a)
+
 def S.widen_high_T_u(a):
     return S.widen_high_T(Zext, a)
 ```

From 5bb3e3acfcf1a8e670920b63ce95115f94365302 Mon Sep 17 00:00:00 2001
From: Thomas Lively <tlively@google.com>
Date: Fri, 13 Sep 2019 11:22:22 -0700
Subject: [PATCH 3/3] Formatting

---
 proposals/simd/SIMD.md | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/proposals/simd/SIMD.md b/proposals/simd/SIMD.md
index 26345cce3..16277829d 100644
--- a/proposals/simd/SIMD.md
+++ b/proposals/simd/SIMD.md
@@ -817,9 +817,6 @@ def S.narrow_T_s(a, b):
         result[T.Lanes + i] = S.SignedSaturate(b[i])
     return result
 
-```
-
-```python
 def S.narrow_T_u(a, b):
     result = S.New()
     for i in range(T.Lanes):
@@ -827,7 +824,6 @@ def S.narrow_T_u(a, b):
     for i in range(T.Lanes):
         result[T.Lanes + i] = S.UnsignedSaturate(b[i])
     return result
-
 ```
 
 ### Integer to integer widening