bdiff: check and cast first parameter value on putbe32() calls

Eliminates

  mercurial/bdiff.c(383) : warning C4244: 'function' : conversion from '__int64'
  to 'uint32_t', possible loss of data
  mercurial/bdiff.c(384) : warning C4244: 'function' : conversion from '__int64'
  to 'uint32_t', possible loss of data
  mercurial/bdiff.c(385) : warning C4244: 'function' : conversion from
  'Py_ssize_t' to 'uint32_t', possible loss of data

when compiling for Windows x64 target using the Microsoft compiler.

mercurial/bdiff.c

@@ -381,9 +381,18 b' static PyObject *bdiff(PyObject *self, P'
 	for (h = l.next; h; h = h->next) {
 		if (h->a1 != la || h->b1 != lb) {
 			len = bl[h->b1].l - bl[lb].l;
-			putbe32(al[la].l - al->l, rb);
-			putbe32(al[h->a1].l - al->l, rb + 4);
-			putbe32(len, rb + 8);
+
+#define checkputbe32(__x, __c) \
+	if (__x > UINT_MAX) { \
+		PyErr_SetString(PyExc_ValueError, \
+		                "bdiff: value too large for putbe32"); \
+		goto nomem; \
+	} \
+	putbe32((uint32_t)(__x), __c);
+
+			checkputbe32(al[la].l - al->l, rb);
+			checkputbe32(al[h->a1].l - al->l, rb + 4);
+			checkputbe32(len, rb + 8);
 			memcpy(rb + 12, bl[lb].l, len);
 			rb += 12 + len;
 		}