Changeset 7421:d1d1db9cb07b

Timestamp:

11/21/07 07:15:44 (6 years ago)

Author:

Martin Albrecht <malb@…>

Branch:

default

Message:

fix #1224 (endianess issue in FiniteField?_nt_gf2e)
untested on big endian machines

File:

• sage/rings/finite_field_ntl_gf2e.pyx (modified) (3 diffs)

sage/rings/finite_field_ntl_gf2e.pyx

@@ -118 +118 @@
     GF = sage.rings.finite_field.GF
 
+cdef extern from "arpa/inet.h":
+    unsigned int htonl(unsigned int)
+
+cdef little_endian():
+    return htonl(1) != 1
+
+cdef unsigned int switch_endianess(unsigned int i):
+    cdef int j
+    cdef unsigned int ret = 0
+    for j from 0 <= j < sizeof(int):
+        (<unsigned char*>&ret)[j] = (<unsigned char*>&i)[sizeof(int)-j-1]
+    return ret
+
 cdef class FiniteField_ntl_gf2e(FiniteField):
     """
@@ -980 +993 @@
             sage: int(a^2 + 1)
             5
-        """
-        cdef unsigned long i = 0
+            sage: k.<a> = GF(2^70)
+            sage: int(a^65 + a^64 + 1)
+            55340232221128654849L
+        """
+        cdef unsigned int i = 0
         ret = int(0)
         cdef unsigned long shift = 0
@@ -989 +1005 @@
             return 0
 
-        while GF2X_deg(r) >= sizeof(long)*8:
-            BytesFromGF2X(<unsigned char *>&i, r, sizeof(long))
+        if little_endian():
+            while GF2X_deg(r) >= sizeof(int)*8:
+                BytesFromGF2X(<unsigned char *>&i, r, sizeof(int))
+                ret += int(i) << shift
+                shift += sizeof(int)*8
+                GF2X_RightShift(r,r,(sizeof(int)*8))
+            BytesFromGF2X(<unsigned char *>&i, r, sizeof(int))
             ret += int(i) << shift
-            shift += sizeof(long)*8
-            GF2X_RightShift(r,r,(sizeof(long)*8))
-
-        BytesFromGF2X(<unsigned char *>&i, r, sizeof(long))
-        ret += int(i) << shift
+        else:
+            while GF2X_deg(r) >= sizeof(int)*8:
+                BytesFromGF2X(<unsigned char *>&i, r, sizeof(int))
+                ret += int(switch_endianess(i)) << shift
+                shift += sizeof(int)*8
+                GF2X_RightShift(r,r,(sizeof(int)*8))
+            BytesFromGF2X(<unsigned char *>&i, r, sizeof(int))
+            ret += int(switch_endianess(i)) << shift
         
         return int(ret)