[gcr: 1/4] gcr: Reverse bit order of usage extension

[Daiki Ueno <dueno src gnome org>]

commit f8acf4e720b2d916f0c0d23d6de77802ce6c679c
Author: Christophe Kamphaus <christophe kamphaus jemmic com>
Date:   Tue Jun 9 00:44:29 2020 +0200

    gcr: Reverse bit order of usage extension
    
    Helps #47

 gcr/gcr-certificate-extensions.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)
---
diff --git a/gcr/gcr-certificate-extensions.c b/gcr/gcr-certificate-extensions.c
index ab62be6..6c17d09 100644
--- a/gcr/gcr-certificate-extensions.c
+++ b/gcr/gcr-certificate-extensions.c
@@ -147,6 +147,18 @@ _gcr_certificate_extension_subject_key_identifier (GBytes *data,
        return result;
 }
 
+static gulong
+_gcr_reverse_bits(gulong num, guint n_bits)
+{
+    gulong reverse_num = 0;
+    guint i;
+    for (i = 0; i < n_bits; i++) {
+        if ((num & (1 << i)))
+            reverse_num |= 1 << ((n_bits - 1) - i);
+    }
+    return reverse_num;
+}
+
 gboolean
 _gcr_certificate_extension_key_usage (GBytes *data,
                                       gulong *key_usage)
@@ -163,6 +175,7 @@ _gcr_certificate_extension_key_usage (GBytes *data,
 
        ret = egg_asn1x_get_bits_as_ulong (asn, key_usage, &n_bits);
        egg_asn1x_destroy (asn);
+       *key_usage = _gcr_reverse_bits(*key_usage, n_bits);
        return ret;
 }