Reduce code size in mbedtls_asn1_write_len
Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/asn1write.c b/library/asn1write.c
index c65d937..1c7f15d 100644
--- a/library/asn1write.c
+++ b/library/asn1write.c
@@ -30,66 +30,33 @@
int mbedtls_asn1_write_len(unsigned char **p, const unsigned char *start, size_t len)
{
- if (len < 0x80) {
- if (*p - start < 1) {
- return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
- }
-
- *--(*p) = (unsigned char) len;
- return 1;
- }
-
- if (len <= 0xFF) {
- if (*p - start < 2) {
- return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
- }
-
- *--(*p) = (unsigned char) len;
- *--(*p) = 0x81;
- return 2;
- }
-
- if (len <= 0xFFFF) {
- if (*p - start < 3) {
- return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
- }
-
- *--(*p) = MBEDTLS_BYTE_0(len);
- *--(*p) = MBEDTLS_BYTE_1(len);
- *--(*p) = 0x82;
- return 3;
- }
-
- if (len <= 0xFFFFFF) {
- if (*p - start < 4) {
- return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
- }
-
- *--(*p) = MBEDTLS_BYTE_0(len);
- *--(*p) = MBEDTLS_BYTE_1(len);
- *--(*p) = MBEDTLS_BYTE_2(len);
- *--(*p) = 0x83;
- return 4;
- }
-
- int len_is_valid = 1;
#if SIZE_MAX > 0xFFFFFFFF
- len_is_valid = (len <= 0xFFFFFFFF);
+ if (len > 0xFFFFFFFF) return MBEDTLS_ERR_ASN1_INVALID_LENGTH;
#endif
- if (len_is_valid) {
- if (*p - start < 5) {
- return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
- }
- *--(*p) = MBEDTLS_BYTE_0(len);
- *--(*p) = MBEDTLS_BYTE_1(len);
- *--(*p) = MBEDTLS_BYTE_2(len);
- *--(*p) = MBEDTLS_BYTE_3(len);
- *--(*p) = 0x84;
- return 5;
+ int required = 1;
+ if (len < 0x80) {
+ required = 1;
+ } else {
+ for (size_t l = len; l != 0; l >>= 8) {
+ required++;
+ }
}
- return MBEDTLS_ERR_ASN1_INVALID_LENGTH;
+ if (required > (*p - start)) {
+ return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
+ }
+
+ do {
+ *--(*p) = MBEDTLS_BYTE_0(len);
+ len >>= 8;
+ } while (len);
+
+ if (required > 1) {
+ *--(*p) = (unsigned char)(required + 0x7f);
+ }
+
+ return required;
}
int mbedtls_asn1_write_tag(unsigned char **p, const unsigned char *start, unsigned char tag)