[Insight-developers] Non-ITK question

[Johnson, Hans J]

Brad or any ITK developers,

I'd like to tap into your vast knowledge about standards and "safe" types.  I received a query with regards to upcoming changes to the NIFTI-2 image file format where we are trying to make it 64bit compatible for large data sets.

Would you mind providing me with a quick response regarding the long-term (say 10 years) safety of depending on sizeof(double) being 8 bytes in C?

 We are already allowing C99 for integer types.

Any recommendations so that we maximize maintainability and portability to next generation 128bit computers?

Thanks,
Hans



On 3/11/11 8:24 AM, "rick reynolds" <reynoldr at mail.nih.gov<mailto:reynoldr at mail.nih.gov>> wrote:

Hi Hans,

Have you run into many issues with sizeof(double) being something
other than 8?  The C standard does not specify sizes for float
types, so I want to be sure use of double will be reliable enough.

Thanks,

- rick


Changes to the header
The changes to the NIfTI header structure are the following (also see below for the full header struct):
    - short dim[8] becomes int64_t dim[8]
    - float intent_p1 becomes double intent_p1
    - float intent_p2 becomes double intent_p2
    - float intent_p3 becomes double intent_p3
    - float pixdim[8] becomes double pixdim[8]
    - float vox_offset becomes int64_t vox_offset
    - float scl_slope becomes double scl_slope
    - float scl_inter becomes double scl_inter
    - float cal_max becomes double cal_max
    - float cal_min becomes double cal_min
    - float slice_duration becomes double slice_duration
    - float toffset becomes double toffset
    - float quatern_b becomes double quatern_b
         and similarly for quatern_c, quatern_d, qoffset_x, qoffset_y, qoffset_z
    - float srow_x[4] becomes double srow_x[4]
         and similarly for srow_y[4], srow_z[4]
    - char magic[4] becomes char magic[8]
    - char unused_str[7] is added at the end of the header
    - removing previously unused fields: data_type, db_name, extents, session_error, regular, glmax, glmin
    - reordering of some of the fields to ensure 8-byte alignments for all doubles



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