Fix small overestimation of base64 encoding output length.

tglsfdc · pull[bot] · commit 7d3aece76619 · 2024-03-08T00:33:49.000Z
pg_base64_enc_len() and its clones overestimated the output length by up to 2 bytes, as a result of sloppy thinking about where to divide. No callers require a precise estimate, so this has no consequences worse than palloc'ing a byte or two more than necessary. We might as well get it right though. This bug is very ancient, dating to commit 79d78bb which added encode.c. (The other instances were presumably copied from there.) Still, it doesn't quite seem worth back-patching. Oleg Tselebrovskiy Discussion: https://postgr.es/m/f94da55286a63022150bc266afdab754@postgrespro.ru
diff --git a/contrib/pgcrypto/pgp-armor.c b/contrib/pgcrypto/pgp-armor.c
@@ -165,7 +165,7 @@ pg_base64_enc_len(unsigned srclen)
 	/*
 	 * 3 bytes will be converted to 4, linefeed after 76 chars
 	 */
-	return (srclen + 2) * 4 / 3 + srclen / (76 * 3 / 4);
+	return (srclen + 2) / 3 * 4 + srclen / (76 * 3 / 4);
 }
 
 static unsigned
diff --git a/src/backend/utils/adt/encode.c b/src/backend/utils/adt/encode.c
@@ -385,7 +385,7 @@ static uint64
 pg_base64_enc_len(const char *src, size_t srclen)
 {
 	/* 3 bytes will be converted to 4, linefeed after 76 chars */
-	return ((uint64) srclen + 2) * 4 / 3 + (uint64) srclen / (76 * 3 / 4);
+	return ((uint64) srclen + 2) / 3 * 4 + (uint64) srclen / (76 * 3 / 4);
 }
 
 static uint64
diff --git a/src/common/base64.c b/src/common/base64.c
@@ -224,7 +224,7 @@ int
 pg_b64_enc_len(int srclen)
 {
 	/* 3 bytes will be converted to 4 */
-	return (srclen + 2) * 4 / 3;
+	return (srclen + 2) / 3 * 4;
 }
 
 /*

Original file line number	Diff line number	Diff line change
`@@ -165,7 +165,7 @@ pg_base64_enc_len(unsigned srclen)`
`165`	`165`	`/*`
`166`	`166`	`* 3 bytes will be converted to 4, linefeed after 76 chars`
`167`	`167`	`*/`
`168`		`- return (srclen + 2) * 4 / 3 + srclen / (76 * 3 / 4);`
	`168`	`+ return (srclen + 2) / 3 * 4 + srclen / (76 * 3 / 4);`
`169`	`169`	`}`
`170`	`170`
`171`	`171`	`static unsigned`
Original file line number	Diff line number	Diff line change
`@@ -385,7 +385,7 @@ static uint64`
`385`	`385`	`pg_base64_enc_len(const char *src, size_t srclen)`
`386`	`386`	`{`
`387`	`387`	`/* 3 bytes will be converted to 4, linefeed after 76 chars */`
`388`		`- return ((uint64) srclen + 2) * 4 / 3 + (uint64) srclen / (76 * 3 / 4);`
	`388`	`+ return ((uint64) srclen + 2) / 3 * 4 + (uint64) srclen / (76 * 3 / 4);`
`389`	`389`	`}`
`390`	`390`
`391`	`391`	`static uint64`
Original file line number	Diff line number	Diff line change
`@@ -224,7 +224,7 @@ int`
`224`	`224`	`pg_b64_enc_len(int srclen)`
`225`	`225`	`{`
`226`	`226`	`/* 3 bytes will be converted to 4 */`
`227`		`- return (srclen + 2) * 4 / 3;`
	`227`	`+ return (srclen + 2) / 3 * 4;`
`228`	`228`	`}`
`229`	`229`
`230`	`230`	`/*`