From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 24 May 2025 18:57:05 +0000 (-0700)
Subject: factor: check unsigned char counts
X-Git-Tag: v9.8~230
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=374f5fdcc1cca96e2ae89168eba7d9f25c4d48c9;p=thirdparty%2Fcoreutils.git

factor: check unsigned char counts

* src/factor.c (MAX_NFACTS): Allow word size of 128 bits,
even if this is only theoretical now.
Check that struct factors’s unsigned char counts won’t overflow.
---

diff --git a/src/factor.c b/src/factor.c
index 54eb9aa92c..2d91e9e4fc 100644
--- a/src/factor.c
+++ b/src/factor.c
@@ -200,8 +200,16 @@ typedef uint64_t UDItype;
 
 #endif
 
-/* 2*3*5*7*11...*101 is 128 bits, and has 26 prime factors */
-#define MAX_NFACTS 26
+/* 2*3*5*7*11...*101 fits in 128 bits, and has 26 prime factors.
+   This code can be extended in the future as needed; show as an example
+   2*3*5*7*11...*193 which fits in 257 bits, and has 44 prime factors.  */
+#if 2 * W_TYPE_SIZE <= 128
+# define MAX_NFACTS 26
+#elif 2 * W_TYPE_SIZE <= 257
+# define MAX_NFACTS 44
+#else
+# error "configuration has a wide word; please update MAX_NFACTS definition"
+#endif
 
 enum
 {
@@ -266,6 +274,13 @@ static mp_limb_t const BIG_POWER_OF_10 =
 enum { LOG_BIG_POWER_OF_10 = 38 };
 #endif
 
+/* Check that struct factors can use unsigned char to record a uuint's
+   prime factor's multiplicity, which is at most 2 * W_TYPE_SIZE - 1.  */
+static_assert (2 * W_TYPE_SIZE - 1 <= UCHAR_MAX);
+
+/* Likewise for recording the number of prime factors.  */
+static_assert (MAX_NFACTS <= UCHAR_MAX);
+
 struct factors
 {
   uuint plarge; /* Can have a single large factor */