diff --git a/str.c b/str.c
index bc95951f..a6c79dc7 100644
--- a/str.c
+++ b/str.c
@@ -43,32 +43,67 @@ char *tohex(char *dstHex, const unsigned char *srcBinary, size_t bytes)
 }
 
 /* Convert nbinary*2 ASCII hex characters [0-9A-Fa-f] to nbinary bytes of data.  Can be used to
-   perform the conversion in-place, eg, fromhex(buf, (char*)buf, n);  Returns -1 if a non-hex-digit
-   character is encountered, otherwise returns the number of binary bytes produced (= nbinary).
-   @author Andrew Bettison <andrew@servalproject.com>
+ * perform the conversion in-place, eg, fromhex(buf, (char*)buf, n);  Returns -1 if a non-hex-digit
+ * character is encountered, otherwise returns the number of binary bytes produced (= nbinary).
+ *
+ * @author Andrew Bettison <andrew@servalproject.com>
  */
 size_t fromhex(unsigned char *dstBinary, const char *srcHex, size_t nbinary)
 {
-  size_t count = 0;
-  while (count != nbinary) {
-    unsigned char high = hexvalue(*srcHex++);
-    if (high & 0xf0) return -1;
-    unsigned char low = hexvalue(*srcHex++);
-    if (low & 0xf0) return -1;
-    dstBinary[count++] = (high << 4) + low;
-  }
-  return count;
+  if (strn_fromhex(dstBinary, nbinary, srcHex, NULL) == nbinary)
+    return nbinary;
+  return -1;
 }
 
-/* Convert nbinary*2 ASCII hex characters [0-9A-Fa-f] followed by a nul '\0' character to nbinary bytes of data.  Can be used to
-   perform the conversion in-place, eg, fromhex(buf, (char*)buf, n);  Returns -1 if a non-hex-digit
-   character is encountered or the character immediately following the last hex digit is not a nul,
-   otherwise returns zero.
-   @author Andrew Bettison <andrew@servalproject.com>
+/* Convert nbinary*2 ASCII hex characters [0-9A-Fa-f] followed by a nul '\0' character to nbinary
+ * bytes of data.  Can be used to perform the conversion in-place, eg, fromhex(buf, (char*)buf, n);
+ * Returns -1 if a non-hex-digit character is encountered or the character immediately following the
+ * last hex digit is not a nul, otherwise returns zero.
+ *
+ * @author Andrew Bettison <andrew@servalproject.com>
  */
 int fromhexstr(unsigned char *dstBinary, const char *srcHex, size_t nbinary)
 {
-  return (fromhex(dstBinary, srcHex, nbinary) == nbinary && srcHex[nbinary * 2] == '\0') ? 0 : -1;
+  const char *p;
+  if (strn_fromhex(dstBinary, nbinary, srcHex, &p) == nbinary && *p == '\0')
+    return 0;
+  return -1;
+}
+
+/* Decode pairs of ASCII hex characters [0-9A-Fa-f] into binary data with an optional upper limit on
+ * the number of binary bytes produced (destination buffer size).  Returns the number of binary
+ * bytes decoded.  If 'afterHex' is not NULL, then sets *afterHex to point to the source character
+ * immediately following the last hex digit consumed.
+ *
+ * Can be used to perform a conversion in-place, eg:
+ *
+ *    strn_fromhex((unsigned char *)buf, n, (const char *)buf, NULL);
+ *
+ * Can also be used to count hex digits without converting, eg:
+ *
+ *    strn_fromhex(NULL, -1, buf, NULL);
+ *
+ * @author Andrew Bettison <andrew@servalproject.com>
+ */
+size_t strn_fromhex(unsigned char *dstBinary, ssize_t dstlen, const char *srcHex, const char **afterHex)
+{
+  unsigned char *dstorig = dstBinary;
+  unsigned char *dstend = dstBinary + dstlen;
+  while (dstlen == -1 || dstBinary < dstend) {
+    int high = hexvalue(srcHex[0]);
+    if (high == -1)
+      break;
+    int low = hexvalue(srcHex[1]);
+    if (low == -1)
+      break;
+    if (dstorig != NULL)
+      *dstBinary = (high << 4) + low;
+    ++dstBinary;
+    srcHex += 2;
+  }
+  if (afterHex)
+    *afterHex = srcHex;
+  return dstBinary - dstorig;
 }
 
 /* Does this whole buffer contain the same value? */
diff --git a/str.h b/str.h
index 3a5d0bc3..ae50a729 100644
--- a/str.h
+++ b/str.h
@@ -64,19 +64,36 @@ extern const char hexdigit[16];
 char *tohex(char *dstHex, const unsigned char *srcBinary, size_t bytes);
 size_t fromhex(unsigned char *dstBinary, const char *srcHex, size_t nbinary);
 int fromhexstr(unsigned char *dstBinary, const char *srcHex, size_t nbinary);
-int is_all_matching(const unsigned char *ptr, size_t len, unsigned char value);
-char *str_toupper_inplace(char *s);
+size_t strn_fromhex(unsigned char *dstBinary, ssize_t dstlen, const char *src, const char **afterp);
 
 #define alloca_tohex(buf,len)           tohex((char *)alloca((len)*2+1), (buf), (len))
 
 __STR_INLINE int hexvalue(char c)
 {
-  if (c >= '0' && c <= '9') return c - '0';
-  if (c >= 'A' && c <= 'F') return c - 'A' + 10;
-  if (c >= 'a' && c <= 'f') return c - 'a' + 10;
+  switch (c) {
+  case '0': return 0;
+  case '1': return 1;
+  case '2': return 2;
+  case '3': return 3;
+  case '4': return 4;
+  case '5': return 5;
+  case '6': return 6;
+  case '7': return 7;
+  case '8': return 8;
+  case '9': return 9;
+  case 'a': case 'A': return 10;
+  case 'b': case 'B': return 11;
+  case 'c': case 'C': return 12;
+  case 'd': case 'D': return 13;
+  case 'e': case 'E': return 14;
+  case 'f': case 'F': return 15;
+  }
   return -1;
 }
 
+int is_all_matching(const unsigned char *ptr, size_t len, unsigned char value);
+char *str_toupper_inplace(char *s);
+
 char *toprint(char *dstStr, ssize_t dstBufSiz, const char *srcBuf, size_t srcBytes, const char quotes[2]);
 char *toprint_str(char *dstStr, ssize_t dstBufSiz, const char *srcStr, const char quotes[2]);
 size_t toprint_len(const char *srcBuf, size_t srcBytes, const char quotes[2]);