1 files changed, 25 insertions, 0 deletions
diff --git a/scan_asn1length.c b/scan_asn1length.c
new file mode 100644
index 0000000..944bd52
--- /dev/null
+++ b/scan_asn1length.c
@@ -0,0 +1,25 @@
+#include <inttypes.h>
+#include "asn1.h"
+
+size_t scan_asn1length(const char* src,const char* max,size_t* length) {
+  const char* orig=src;
+  if (src>=max) return 0;
+/* If the highest bit of the first byte is clear, the byte is the length.
+ * Otherwise the next n bytes are the length (n being the lower 7 bits) */
+  if (*src&0x80) {
+    int chars=*src&0x7f;
+    size_t l=0;
+    while (chars>0) {
+      if (++src>=max) return 0;
+      if (l>(((unsigned long)-1)>>8)) return 0;	/* catch integer overflow */
+      l=l*256+(unsigned char)*src;
+      --chars;
+    }
+    *length=l;
+  } else
+    *length=*src&0x7f;
+  src++;
+  if (src+*length>max) return 0;	/* catch integer overflow */
+  if ((uintptr_t)src+*length<(uintptr_t)src) return 0;	/* gcc 4.1 removes this check without the cast to uintptr_t */
+  return src-orig;
+}