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function fits_test_checksum,hdr, data, ERRMSG = errmsg,FROM_IEEE=from_ieee |
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;+ |
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; NAME: |
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; FITS_TEST_CHECKSUM() |
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; PURPOSE: |
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; Verify the values of the CHECKSUM and DATASUM keywords in a FITS header |
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; EXPLANATION: |
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; Follows the 23 May 2002 version of the FITS checksum proposal at |
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; http://heasarc.gsfc.nasa.gov/docs/heasarc/fits/checksum.html |
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; |
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; CALLING SEQUENCE: |
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; result = FITS_TEST_CHECKSUM(HDR, [ DATA, ERRMSG=, /FROM_IEEE ]) |
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; INPUTS: |
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; HDR - FITS header (vector string) |
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; OPTIONAL DATA: |
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; DATA - data array associated with the FITS header. If not supplied, or |
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; set to a scalar, then there is assumed to be no data array |
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; associated with the FITS header. |
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; RESULT: |
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; An integer -1, 0 or 1 indicating the following conditions: |
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; 1 - CHECKSUM (and DATASUM) keywords are present with correct values |
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; 0 - CHECKSUM keyword is not present |
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; -1 - CHECKSUM or DATASUM keyword does not have the correct value |
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; indicating possible data corruption. |
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; OPTIONAL INPUT KEYWORD: |
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; /FROM_IEEE - If this keyword is set, then the input is assumed to be in |
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; big endian format (e.g. an untranslated FITS array). This |
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; keyword only has an effect on little endian machines (e.g. |
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; a Linux box). |
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; OPTIONAL OUTPUT KEYWORD: |
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; ERRMSG - will contain a scalar string giving the error condition. If |
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; RESULT = 1 then ERRMSG will be an empty string. If this |
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; output keyword is not supplied, then the error message will be |
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; printed at the terminal. |
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; NOTES: |
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; The header and data must be *exactly* as originally written in the FITS |
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; file. By default, some FITS readers may alter keyword values (e.g. |
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; BSCALE) or append information (e.g. HISTORY or an inherited primary |
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; header) and this will alter the checksum value. |
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; PROCEDURES USED: |
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; CHECKSUM32, FITS_ASCII_ENCODE(), SXPAR() |
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; EXAMPLE: |
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; Verify the CHECKSUM keywords in the primary header/data unit of a FITS |
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; file 'test.fits' |
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; |
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; FITS_READ,'test.fits',data,hdr,/no_PDU,/NoSCALE |
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; print,FITS_TEST_CHECKSUM(hdr,data) |
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; |
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; Note the use of the /No_PDU and /NoSCALE keywords to avoid any alteration |
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; of the FITS header |
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; REVISION HISTORY: |
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; W. Landsman SSAI December 2002 |
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; Return quietly if CHECKSUM keywords not found W. Landsman May 2003 |
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; Add /NOSAVE to CHECKSUM32 calls when possible W. Landsman Sep 2004 |
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;- |
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if N_Params() LT 1 then begin |
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print,'Syntax - result = FITS_TEST_CHECKSUM(Hdr, [Data,' + $ |
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' ERRMSG=, /FROM_IEEE ])' |
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return, 0 |
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endif |
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result = 1 |
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printerr = not arg_present(errmsg) |
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checksum = sxpar(hdr,'CHECKSUM', Count = N_checksum) |
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datasum = sxpar(hdr,'DATASUM', Count = N_datasum) |
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if (N_checksum EQ 0) then begin |
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errmsg = 'CHECKSUM keyword not present in FITS header' |
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if printerr then message,/con, errmsg |
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return, 0 |
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endif |
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if N_datasum EQ 0 then datasum = '0' |
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ch = shift(byte(checksum),-1) |
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checksum32,ch-48b, sum32, /NOSAVE |
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bhdr = byte(hdr) |
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remain = N_elements(bhdr) mod 2880 |
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if remain NE 0 then $ |
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bhdr = [reform(bhdr,N_elements(bhdr)), replicate(32b, 2880 - remain) ] |
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checksum32,bhdr, hsum, FROM_IEEE = from_ieee, /NOSAVE |
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Ndata = N_elements(data) |
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if Ndata GT 1 then begin |
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checksum32, data, dsum, FROM_IEEE= from_ieee |
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remain = Ndata mod 2880 |
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if remain GT 0 then begin |
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exten = sxpar( hdr, 'XTENSION', Count = N_exten) |
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if N_exten GT 0 then if exten EQ 'TABLE ' then $ |
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checksum32,[dsum,replicate(32b,2880-remain)],dsum,/NOSAVE |
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endif |
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checksum32, [dsum, hsum], hdusum, /NOSAVE |
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dsum = strtrim(dsum,2) |
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if dsum NE datasum then begin |
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result = 1 |
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errmsg = 'Computed Datasum: ' + dsum + $ |
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' FITS header value: ' + datasum |
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if printerr then message,/Con, errmsg |
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endif |
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endif else hdusum = hsum |
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|
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csum = FITS_ASCII_ENCODE(not hdusum) |
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if csum NE '0000000000000000' then begin |
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result = -1 |
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errmsg = 'Computed Checksum: ' + csum + $ |
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' FITS header value: ' + checksum |
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if printerr then message,/Con, errmsg |
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endif |
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return, result |
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end |
