Fixes/comments for guessBestEncoding (#304)

* tests: add case for getRecommendedEncoding

* vmime: avoid integer multiply wraparound in wordEncoder::guessBestEncoding

If the input string is 42949673 characters long or larger, there will
be integer overflow on 32-bit platforms when multiplying by 100.
Switch that one computation to floating point.

* vmime: update comment in wordEncoder::guessBestEncoding

1 files changed, 6 insertions, 4 deletions

diff --git a/src/vmime/wordEncoder.cpp b/src/vmime/wordEncoder.cpp
index 4f47d047..d1632022 100644
--- a/src/vmime/wordEncoder.cpp
+++ b/src/vmime/wordEncoder.cpp
@@ -302,14 +302,16 @@ wordEncoder::Encoding wordEncoder::guessBestEncoding(
 		}
 	}
 
-	// Use Base64 if more than 40% non-ASCII, or Quoted-Printable else (default)
+	// Base64 would be more space-efficient when the ASCII content is
+	// below 83.33%, but QP has a legibility arugment going for it, so we
+	// picked 60%.
 	const size_t asciiCount =
 		utility::stringUtils::countASCIIchars(buffer.begin(), buffer.end());
 
-	const size_t asciiPercent =
-		buffer.length() == 0 ? 100 : (100 * asciiCount) / buffer.length();
+	const double asciiPercent =
+		buffer.length() == 0 ? 100 : static_cast<double>(asciiCount) / buffer.length();
 
-	if (asciiPercent < 60) {
+	if (asciiPercent < 0.60) {
 		return ENCODING_B64;
 	} else {
 		return ENCODING_QP;