Introduce a locale-independent version of isdigit

While information is contradictory on this subject, investigation
of several implementaions and Posix appears to indicate that it
is possible to change the behaviour of isdigit() with locale.

Change-Id: I6ba9ecbb5563d04d41c54dd071e86b2354483f77
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/56625
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

crypto/bn_extra/convert.c

@@ -310,7 +310,7 @@ err:
 }
 
 int BN_dec2bn(BIGNUM **outp, const char *in) {
-  return bn_x2bn(outp, in, decode_dec, isdigit);
+  return bn_x2bn(outp, in, decode_dec, OPENSSL_isdigit);
 }
 
 int BN_asc2bn(BIGNUM **outp, const char *in) {

crypto/bytestring/cbs.c

@@ -232,7 +232,7 @@ int CBS_get_u64_decimal(CBS *cbs, uint64_t *out) {
   int seen_digit = 0;
   while (CBS_len(cbs) != 0) {
     uint8_t c = CBS_data(cbs)[0];
-    if (!isdigit(c)) {
+    if (!OPENSSL_isdigit(c)) {
       break;
     }
     CBS_skip(cbs, 1);
@@ -753,13 +753,13 @@ static int cbs_get_two_digits(CBS *cbs, int *out) {
   if (!CBS_get_u8(cbs, &first_digit)) {
     return 0;
   }
-  if (!isdigit(first_digit)) {
+  if (!OPENSSL_isdigit(first_digit)) {
     return 0;
   }
   if (!CBS_get_u8(cbs, &second_digit)) {
     return 0;
   }
-  if (!isdigit(second_digit)) {
+  if (!OPENSSL_isdigit(second_digit)) {
     return 0;
   }
   *out = (first_digit - '0') * 10 + (second_digit - '0');

crypto/mem.c

@@ -308,6 +308,10 @@ char *OPENSSL_strdup(const char *s) {
   return ret;
 }
 
+int OPENSSL_isdigit(int c) {
+  return c >= '0' && c <= '9';
+}
+
 int OPENSSL_tolower(int c) {
   if (c >= 'A' && c <= 'Z') {
     return c + ('a' - 'A');

include/openssl/mem.h

@@ -110,6 +110,10 @@ OPENSSL_EXPORT char *OPENSSL_strdup(const char *s);
 // OPENSSL_strnlen has the same behaviour as strnlen(3).
 OPENSSL_EXPORT size_t OPENSSL_strnlen(const char *s, size_t len);
 
+// OPENSSL_isdigit is a locale-independent version of isdigit(3), It
+// only recognizes '0' through '9' as digits.
+OPENSSL_EXPORT int OPENSSL_isdigit(int c);
+
 // OPENSSL_tolower is a locale-independent version of tolower(3). It only
 // lowercases ASCII values. Other values are returned as-is.
 OPENSSL_EXPORT int OPENSSL_tolower(int c);

ssl/test/test_config.cc

@@ -63,7 +63,7 @@ bool StringToInt(T *out, const char *str) {
 
   // |strtoull| allows leading '-' with wraparound. Additionally, both
   // functions accept empty strings and leading whitespace.
-  if (!isdigit(static_cast<unsigned char>(*str)) &&
+  if (!OPENSSL_isdigit(static_cast<unsigned char>(*str)) &&
       (!std::is_signed<T>::value || *str != '-')) {
     return false;
   }