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diff --git a/subprojects/exess/src/string_utils.h b/subprojects/exess/src/string_utils.h
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+++ b/subprojects/exess/src/string_utils.h
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+/*
+  Copyright 2011-2021 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#ifndef EXESS_STRING_UTILS_H
+#define EXESS_STRING_UTILS_H
+
+#include <stdbool.h>
+
+/// Return true if `c` lies within [`min`...`max`] (inclusive)
+static inline bool
+in_range(const int c, const int min, const int max)
+{
+  return (c >= min && c <= max);
+}
+
+/// Return true if `c` is a whitespace character
+static inline bool
+is_space(const int c)
+{
+  switch (c) {
+  case ' ':
+  case '\f':
+  case '\n':
+  case '\r':
+  case '\t':
+  case '\v':
+    return true;
+  default:
+    return false;
+  }
+}
+
+/// ALPHA ::= [A-Za-z]
+static inline bool
+is_alpha(const int c)
+{
+  return in_range(c, 'A', 'Z') || in_range(c, 'a', 'z');
+}
+
+/// DIGIT ::= [0-9]
+static inline bool
+is_digit(const int c)
+{
+  return in_range(c, '0', '9');
+}
+
+/// HEXDIG ::= DIGIT | "A" | "B" | "C" | "D" | "E" | "F"
+static inline bool
+is_hexdig(const int c)
+{
+  return is_digit(c) || in_range(c, 'A', 'F');
+}
+
+/// BASE64 ::= ALPHA | DIGIT | "+" | "/" | "="
+static inline bool
+is_base64(const int c)
+{
+  return is_alpha(c) || is_digit(c) || c == '+' || c == '/' || c == '=';
+}
+
+#endif // EXESS_STRING_UTILS_H