RF - replace flt2nmant with type_info

Use type_info nmant estimate.

Author: matthew-brett

nibabel/casting.py

@@ -249,26 +249,7 @@ def flt2nmant(flt_type):
         return _flt_nmant[flt_type]
     except KeyError:
         pass
-    fi = np.finfo(flt_type)
-    nmant, nexp = fi.nmant, fi.nexp
-    # Assuming the np.float type is always IEEE 64 bit
-    if flt_type is np.float and (nmant, nexp) == (52, 11):
-        return 52
-    # Now we should be testing long doubles
-    assert flt_type is np.longdouble
-    if (nmant, nexp) == (63, 15): # 80-bit intel type
-        return 63 # Not including explicit first digit
-    # We test the declared nmant by stepping up and down.  These tests assume a
-    # binary format
-    i_end_contig = 2**(nmant+1) # int
-    f_end_contig = flt_type(i_end_contig)
-    # We need as_int here because long doubles do not necessarily convert
-    # correctly to ints with int() - see
-    # http://projects.scipy.org/numpy/ticket/1395
-    if as_int(f_end_contig-1) == (i_end_contig-1): # still representable
-        if as_int(f_end_contig+1) == i_end_contig: # Rounding down
-            return nmant
-    raise FloatingError('Cannot be confident of nmant value for %s' % flt_type)
+    return type_info(flt_type)['nmant']
 
 
 def as_int(x, check=True):