Closes #15908: SHA1 crashes in 64 bits when the string to hash is bigger than 2**32 bytes
diff --git a/Modules/shamodule.c b/Modules/shamodule.c
index a86e722..df73441 100644
--- a/Modules/shamodule.c
+++ b/Modules/shamodule.c
@@ -536,6 +536,8 @@
     static char *kwlist[] = {"string", NULL};
     SHAobject *new;
     Py_buffer view = { 0 };
+    Py_ssize_t n;
+    unsigned char *buf;
 
     if (!PyArg_ParseTupleAndKeywords(args, kwdict, "|s*:new", kwlist,
                                      &view)) {
@@ -554,10 +556,21 @@
         PyBuffer_Release(&view);
         return NULL;
     }
-    if (view.len > 0) {
-        sha_update(new, (unsigned char*)view.buf,
-                   Py_SAFE_DOWNCAST(view.len, Py_ssize_t, unsigned int));
+
+    n = view.len;
+    buf = (unsigned char *) view.buf;
+    while (n > 0) {
+        Py_ssize_t nbytes;
+        if (n > INT_MAX)
+            nbytes = INT_MAX;
+        else
+            nbytes = n;
+        sha_update(new, buf,
+                   Py_SAFE_DOWNCAST(nbytes, Py_ssize_t, unsigned int));
+        buf += nbytes;
+        n -= nbytes;
     }
+
     PyBuffer_Release(&view);
 
     return (PyObject *)new;