From 180a565ffb443a3c9430bd04e7bbb1963e239412 Mon Sep 17 00:00:00 2001
From: Nick Bowler <nbowler@draconx.ca>
Date: Wed, 25 Oct 2023 20:59:16 -0400
Subject: [PATCH] libcdecl: Avoid snprintf for integer conversions.

To reduce the library dependency on gnulib replacements, implement the
conversion of uintmax_t to decimal by simple repeated division.  This
way avoids any need to worry about whether the C library can actually
perform 64-bit decimal conversions properly.
---
 src/cdecl-internal.h |  1 +
 src/declare.c        |  3 +--
 src/explain.c        |  3 +--
 src/output.c         | 35 +++++++++++++++++++++++++++++++++++
 4 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/src/cdecl-internal.h b/src/cdecl-internal.h
index 0d8f2e8..186c6b0 100644
--- a/src/cdecl-internal.h
+++ b/src/cdecl-internal.h
@@ -81,6 +81,7 @@ struct output_state {
 
 size_t cdecl__advance(struct output_state *dst, size_t amount);
 size_t cdecl__emit(struct output_state *dst, const char *src);
+size_t cdecl__emit_uint(struct output_state *dst, uintmax_t val);
 size_t cdecl__strlcpy(char *dst, const char *src, size_t len);
 
 const char *cdecl__emit_specs(struct output_state *dst,
diff --git a/src/declare.c b/src/declare.c
index 119d2b2..172c0a9 100644
--- a/src/declare.c
+++ b/src/declare.c
@@ -72,8 +72,7 @@ static void declare_array(struct output_state *dst, struct cdecl_array *a)
 		const char *s = a->vla[0] ? a->vla : "*";
 		cdecl__emit(dst, s);
 	} else {
-		size_t rc = snprintf(dst->dst, dst->dstlen, "%.0" PRIuMAX, a->length);
-		cdecl__advance(dst, rc);
+		cdecl__emit_uint(dst, a->length);
 	}
 
 	cdecl__emit(dst, "]");
diff --git a/src/explain.c b/src/explain.c
index a22b4d0..6d6aa87 100644
--- a/src/explain.c
+++ b/src/explain.c
@@ -76,8 +76,7 @@ explain_array(struct output_state *dst, struct cdecl_array *a)
 	if (a->vla) {
 		rc = cdecl__emit(dst, a->vla);
 	} else {
-		rc = snprintf(dst->dst, dst->dstlen, "%.0" PRIuMAX, a->length);
-		cdecl__advance(dst, rc);
+		rc = cdecl__emit_uint(dst, a->length);
 	}
 
 	cdecl__emit(dst, " of " + !rc);
diff --git a/src/output.c b/src/output.c
index 7206eb9..047fc64 100644
--- a/src/output.c
+++ b/src/output.c
@@ -51,6 +51,41 @@ size_t cdecl__emit(struct output_state *dst, const char *src)
 	return cdecl__advance(dst, rc);
 }
 
+/*
+ * 31 decimal digits is enough for values up to 2^102 - 1.
+ * 63 decimal digits is enough for values up to 2^209 - 1.
+ *
+ * We can't portably write numbers this large in preprocessor conditionals,
+ * but since the maximum values of unsigned integer types are always one
+ * less than a power of two, we can use a sequence of small shifts to infer
+ * the bounds.
+ *
+ * All known implementations have 64-bit uintmax_t.  Leave some headroom
+ * to support a possible future implementatons with 128-bit uintmax_t.
+ */
+enum {
+#if (UINTMAX_MAX >> 27 >> 27 >> 26 >> 26) == 0
+	MAX_UINT_DIGITS = 31
+#elif (UINTMAX_MAX >> 27 >> 26 >> 26 >> 26 >> 26 >> 26 >> 26 >> 26) == 0
+	MAX_UINT_DIGITS = 63
+#else
+#	error UINTMAX_MAX is too large, please report a bug.
+#endif
+};
+
+size_t cdecl__emit_uint(struct output_state *dst, uintmax_t val)
+{
+	char buf[MAX_UINT_DIGITS + 1], *p = &buf[sizeof buf];
+
+	*(--p) = 0;
+	while (val > 0) {
+		*(--p) = '0' + val % 10;
+		val /= 10;
+	}
+
+	return cdecl__emit(dst, p);
+}
+
 static void explain_spec(struct output_state *dst, struct cdecl_declspec *s)
 {
 	size_t rc;
-- 
2.43.2