1 files changed, 38 insertions, 2 deletions
diff --git a/secore/marshall.py b/secore/marshall.py
index 8f1caee..ebcc71d 100644
--- a/secore/marshall.py
+++ b/secore/marshall.py
@@ -21,14 +21,50 @@ r"""marshall.py: Marshal values into strings
 __docformat__ = "restructuredtext en"
 
 import math
-import xapian
+
+def _long_to_base256_array(value, length, flip):
+    result = []
+    for i in xrange(length):
+        n = value % 256
+        if flip: n = 255 - n
+        result.insert(0, chr(n))
+        value /= 256
+    return result
 
 def float_to_string(value):
     """Marshall a floating point number to a string which sorts in the
     appropriate manner.
 
     """
-    return xapian.sortable_serialise(value)
+    mantissa, exponent = math.frexp(value)
+    sign = '1'
+    if mantissa < 0:
+        mantissa = -mantissa
+        sign = '0'
+
+    # IEEE representation of doubles uses 11 bits for the exponent, with a bias
+    # of 1023.  There's then another 52 bits in the mantissa, so we need to
+    # add 1075 to be sure that the exponent won't be negative.
+    # Even then, we check that the exponent isn't negative, and consider the
+    # value to be equal to zero if it is.
+    exponent += 1075
+    if exponent < 0: # Note - this can't happen on most architectures #pragma: no cover
+        exponent = 0
+        mantissa = 0
+    elif mantissa == 0:
+        exponent = 0
+
+    # IEEE representation of doubles uses 52 bits for the mantissa.  Convert it
+    # to a 7 character string, and convert the exponent to a 2 character
+    # string.
+
+    mantissa = long(mantissa * (2**52))
+
+    digits = [sign]
+    digits.extend(_long_to_base256_array(exponent, 2, sign == '0'))
+    digits.extend(_long_to_base256_array(mantissa, 7, sign == '0'))
+
+    return ''.join(digits)
 
 def date_to_string(date):
     """Marshall a date to a string which sorts in the appropriate manner.