From fa7476a1ee3cd8907928809f8af44285d685c830 Mon Sep 17 00:00:00 2001
From: Konstantin Makarchev <kostya27@gmail.com>
Date: Thu, 27 May 2021 23:39:49 +0300
Subject: [PATCH 1/2] fixed #10751, Base64, exclude last 3 bytes from bswap(for
 correct memory access), and process them manually

---
 src/base64.cr | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/base64.cr b/src/base64.cr
index 9f05145d6f22..19d6fbc689eb 100644
--- a/src/base64.cr
+++ b/src/base64.cr
@@ -203,7 +203,8 @@ module Base64
     bytes = chars.to_unsafe
     size = data.size
     cstr = data.to_unsafe
-    endcstr = cstr + size - size % 3
+    endcstr = cstr + size - size % 3 - 3
+
     while cstr < endcstr
       n = Intrinsics.bswap32(cstr.as(UInt32*).value)
       yield bytes[(n >> 26) & 63]
@@ -213,6 +214,20 @@ module Base64
       cstr += 3
     end
 
+    if size >= 3
+      a = cstr.value
+      b = (cstr + 1).value
+      c = (cstr + 2).value
+      n = (a.to_u32 << 0x10) + (b.to_u32 << 0x08) + c
+
+      yield bytes[(n >> 18) & 63]
+      yield bytes[(n >> 12) & 63]
+      yield bytes[(n >> 6) & 63]
+      yield bytes[(n) & 63]
+
+      cstr += 3
+    end
+
     pd = size % 3
     if pd == 1
       n = (cstr.value.to_u32 << 16)

From f2fddc60d711e6f13fc77109455978fd737f8761 Mon Sep 17 00:00:00 2001
From: Konstantin Makarchev <kostya27@gmail.com>
Date: Fri, 28 May 2021 13:28:50 +0300
Subject: [PATCH 2/2] add comment

---
 src/base64.cr | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/src/base64.cr b/src/base64.cr
index 19d6fbc689eb..36bb482d5634 100644
--- a/src/base64.cr
+++ b/src/base64.cr
@@ -205,6 +205,7 @@ module Base64
     cstr = data.to_unsafe
     endcstr = cstr + size - size % 3 - 3
 
+    # process bunch of full triples
     while cstr < endcstr
       n = Intrinsics.bswap32(cstr.as(UInt32*).value)
       yield bytes[(n >> 26) & 63]
@@ -214,20 +215,17 @@ module Base64
       cstr += 3
     end
 
+    # process last full triple manually, because reading UInt32 not correct for guarded memory
     if size >= 3
-      a = cstr.value
-      b = (cstr + 1).value
-      c = (cstr + 2).value
-      n = (a.to_u32 << 0x10) + (b.to_u32 << 0x08) + c
-
+      n = (cstr.value.to_u32 << 16) | ((cstr + 1).value.to_u32 << 8) | (cstr + 2).value
       yield bytes[(n >> 18) & 63]
       yield bytes[(n >> 12) & 63]
       yield bytes[(n >> 6) & 63]
       yield bytes[(n) & 63]
-
       cstr += 3
     end
 
+    # process last partial triple
     pd = size % 3
     if pd == 1
       n = (cstr.value.to_u32 << 16)