From ed45fcae676d4039798e7eb6bfcbebdbcc642833 Mon Sep 17 00:00:00 2001
From: Pentarctagon <pentarctagon@tutamail.com>
Date: Tue, 23 May 2023 17:39:51 -0500
Subject: [PATCH] Implement one part of the -Wshorten-64-to-32 changes from
 #7451

Mainly since it's particularly non-obvious why it currently works for `generic_decode_be()` in the case when `in.find_last_not_of("=")` doesn't find anything:
* It returns npos, which is the max value of an std::size_t
* this turns into -1 when assigned to an int
* -1 + 1 equals 0
* 0 * 8 / 6 is still 0
* `reserve(0)` is pointless, but at least valid
This is not a behavior change because it already returns nothing after it does all its work if `out.size()` doesn't equal 0 in this case.

And for `generic_decode_le()` in the case when `in.find_last_not_of("=")` doesn't find anything:
* It returns npos, which is the max value of an std::size_t
* this turns into -1 when assigned to an int
* -1 * 8 / 6 is -0.75, which truncates to 0 because this is integer division
* `reserve(0)` is pointless, but at least valid
This is not a behavior change since the for-loop starts i at 0 and then checks that `i <= last_char`, however last_char is -1 so the loop is just skipped.
---
 src/serialization/base64.cpp | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/src/serialization/base64.cpp b/src/serialization/base64.cpp
index 390bd1e0130..f8794493ecb 100644
--- a/src/serialization/base64.cpp
+++ b/src/serialization/base64.cpp
@@ -52,9 +52,12 @@ char itoa(unsigned value, const std::string& map)
 
 std::vector<uint8_t> generic_decode_be(std::string_view in, const std::vector<int>& atoi_map)
 {
-	const int last_char = in.find_last_not_of("=");
-	const int num_chars = last_char + 1;
-	const int length = num_chars * 6 / 8;
+	const std::size_t last_char = in.find_last_not_of("=");
+	if(last_char == std::string::npos) {
+		return {};
+	}
+	const std::size_t num_chars = last_char + 1;
+	const std::size_t length = num_chars * 6 / 8;
 
 	std::vector<uint8_t> out;
 	out.reserve(length);
@@ -77,7 +80,7 @@ std::vector<uint8_t> generic_decode_be(std::string_view in, const std::vector<in
 			val &= 0xFFFF; // Prevent shifting bits off the left end, which is UB
 		}
 	}
-	if(static_cast<int>(out.size()) != length) {
+	if(out.size() != length) {
 		return {};
 	}
 
@@ -86,13 +89,16 @@ std::vector<uint8_t> generic_decode_be(std::string_view in, const std::vector<in
 
 std::vector<uint8_t> generic_decode_le(std::string_view in, const std::vector<int>& atoi_map)
 {
-	const int last_char = in.find_last_not_of("=");
-	const int length = last_char * 6 / 8;
+	const std::size_t last_char = in.find_last_not_of("=");
+	if(last_char == std::string::npos) {
+		return {};
+	}
+	const std::size_t length = last_char * 6 / 8;
 
 	std::vector<uint8_t> out;
 	out.reserve(length);
 
-	for(int i = 0; i <= last_char; i += 4) {
+	for(std::size_t i = 0; i <= last_char; i += 4) {
 		//add first char (always)
 		unsigned value = atoi_map[in[i]];