bpf: simplify tnum output if a fully known constant

Emit tnum representation as just a constant if all bits are known.
Use decimal-vs-hex logic to determine exact format of emitted
constant value, just like it's done for register range values.
For that move tnum_strn() to kernel/bpf/log.c to reuse decimal-vs-hex
determination logic and constants.

Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231202175705.885270-12-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/log.c

@@ -539,6 +539,19 @@ static void verbose_snum(struct bpf_verifier_env *env, s64 num)
 		verbose(env, "%#llx", num);
 }
 
+int tnum_strn(char *str, size_t size, struct tnum a)
+{
+	/* print as a constant, if tnum is fully known */
+	if (a.mask == 0) {
+		if (is_unum_decimal(a.value))
+			return snprintf(str, size, "%llu", a.value);
+		else
+			return snprintf(str, size, "%#llx", a.value);
+	}
+	return snprintf(str, size, "(%#llx; %#llx)", a.value, a.mask);
+}
+EXPORT_SYMBOL_GPL(tnum_strn);
+
 static void print_scalar_ranges(struct bpf_verifier_env *env,
 				const struct bpf_reg_state *reg,
 				const char **sep)