libcdecl: Avoid snprintf for integer conversions.

[cdecl99.git] / src / output.c

diff --git a/src/output.c b/src/output.c
index 7206eb9b51f46e64026657325d75f27255bfde7a..047fc64ed087138d0d0ceb305485a54d88b0c89d 100644 (file)
--- 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;