From: Mark Wooding <mdw@distorted.org.uk>
Date: Thu, 11 May 2017 09:42:15 +0000 (+0100)
Subject: bytestring.c, catacomb/__init__.py: Introduce and use `zero' method.
X-Git-Tag: 1.2.0~15
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~mdw/git/catacomb-python/commitdiff_plain/5a8b43b3b20b540f20877f14ecb9cb0dae8ddaf3

bytestring.c, catacomb/__init__.py: Introduce and use `zero' method.

Seems like strings of zero bytes are especially useful.  Add a class
method to `ByteString' to generate them efficiently, and use it to make
the magic `Z128' constant.
---

diff --git a/bytestring.c b/bytestring.c
index 6dc70f7..2b74648 100644
--- a/bytestring.c
+++ b/bytestring.c
@@ -73,6 +73,17 @@ end:
   return (0);
 }
 
+static PyObject *meth__ByteString_zero(PyObject *me, PyObject *arg)
+{
+  size_t sz;
+  PyObject *rc = 0;
+  if (!PyArg_ParseTuple(arg, "OO&:zero", &me, convszt, &sz)) goto end;
+  rc = bytestring_pywrap(0, sz);
+  memset(PyString_AS_STRING(rc), 0, sz);
+end:
+  return (rc);
+}
+
 static PyObject *bytestring_pyrichcompare(PyObject *me,
 					  PyObject *you, int op)
 {
@@ -228,6 +239,7 @@ static PyTypeObject bytestring_pytype_skel = {
 static PyMethodDef methods[] = {
 #define METHNAME(func) meth_##func
   METH  (ctstreq,		"ctstreq(S, T) -> BOOL")
+  METH	(_ByteString_zero,	"zero(N) -> 0000...00")
 #undef METHNAME
   { 0 }
 };
diff --git a/catacomb/__init__.py b/catacomb/__init__.py
index 860cfb5..d4eac30 100644
--- a/catacomb/__init__.py
+++ b/catacomb/__init__.py
@@ -56,7 +56,8 @@ def _init():
   for i in b:
     if i[0] != '_':
       d[i] = b[i];
-  for i in ['MP', 'GF', 'Field',
+  for i in ['ByteString',
+            'MP', 'GF', 'Field',
             'ECPt', 'ECPtCurve', 'ECCurve', 'ECInfo',
             'DHInfo', 'BinDHInfo', 'RSAPriv', 'BBSPriv',
             'PrimeFilter', 'RabinMiller',
@@ -738,7 +739,7 @@ _augment(KCDSAPriv, _tmp)
 X25519_BASE = MP(9).storel(32)
 X448_BASE = MP(5).storel(56)
 
-Z128 = bytes('00000000000000000000000000000000')
+Z128 = ByteString.zero(16)
 
 class _BoxyPub (object):
   def __init__(me, pub, *args, **kw):