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C----------------------------------------------------------------------
logical function fttdnn(value)
C test if a R*8 value has a IEEE Not-a-Number value
C A NaN has all the exponent bits=1, and the fractional part
C not=0.
C Exponent field is in bits 20-30 in the most significant 4-byte word
C Mantissa field is in bits 0-19 of most sig. word and entire 2nd word
C
C written by Wm Pence, HEASARC/GSFC, May 1992
C modified Aug 1994 to handle all IEEE special values.
integer value(2)
C COMMON BLOCK DEFINITIONS:--------------------------------------------
integer nb,ne
parameter (nb = 20)
parameter (ne = 200)
integer bufnum,chdu,hdutyp,maxhdu,hdstrt,hdend,nxthdr,dtstrt
integer nxtfld
logical wrmode
common/ft0001/bufnum(199),chdu(nb),hdutyp(nb),maxhdu(nb),
& wrmode(nb),hdstrt(nb,ne),hdend(nb),nxthdr(nb),dtstrt(nb),nxtfld
integer compid
common/ftcpid/compid
C END OF COMMON BLOCK DEFINITIONS-----------------------------------
integer word1,word2
C COMPID specifies what type of floating point word structure
C is used on this machine, and determines how to test for NaNs.
C COMPID value:
C 1 generic machine: simply test for NaNs with all bits set
C 2 like a decstation or alpha OSF/1, or IBM PC
C 3 SUN workstation, or IBM mainframe
C -2305843009213693952 Cray (64-bit) machine
fttdnn=.false.
return
if (compid .eq. 1)then
C on the VAX we can assume that all NaNs will be set to all bits on
C (which is equivalent to an integer with a value of -1) because
C this is what the IEEE to VAX conversion MACRO program returns
if (value(1) .eq. -1 .and. value(2) .eq. -1)fttdnn=.true.
else if (compid .gt. 1)then
if (compid .ge. 3)then
C this is for SUN-like machines, or IBM main frames
word1=value(1)
word2=value(2)
else
C this is for DECstation and IBM PCs. The 2 32 bit integer words
C are reversed from what you get on the SUN.
word1=value(2)
word2=value(1)
end if
C efficiently search the number space for NaNs and underflows
if (word2 .eq. -1)then
if ((word1 .ge. -1048577 .and. word1 .le. -1)
& .or. (word1 .ge. 2146435071))then
fttdnn=.true.
else if ((word1 .lt. -2146435072) .or.
& (word1 .ge. 0 .and. word1 .lt. 1048576))then
value(1)=0
value(2)=0
end if
else if (word2 .eq. 0)then
if ((word1 .gt. -1048577 .and. word1 .le. -1)
& .or. (word1 .gt. 2146435071))then
fttdnn=.true.
else if ((word1 .le. -2146435072) .or.
& (word1 .ge. 0 .and. word1 .le. 1048576))then
value(1)=0
value(2)=0
end if
else
if ((word1 .gt. -1048577 .and. word1 .le. -1)
& .or. (word1 .gt. 2146435071))then
fttdnn=.true.
else if ((word1 .lt. -2146435072) .or.
& (word1 .ge. 0 .and. word1 .lt. 1048576))then
value(1)=0
value(2)=0
end if
end if
else
C branch for the Cray: COMPID stores the negative integer
C which corresponds to the 3 most sig digits set to 1. If these
C 3 bits are set in a floating point number, then it represents
C a reserved value (i.e., a NaN)
if (value(1).lt. 0 .and. value(1) .ge. compid)fttdnn=.true.
end if
end
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