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[email protected] |

To |
[email protected] |

Subject |
st: Floating-point reals, hexadecimal and decimals |

Date |
Wed, 2 Jul 2003 18:21:47 -0400 |

This is a Stata and Perl question. I am generating a Perl module to read Stata data files and I need some clarification with regard to the conversion of floating-point numbers into decimal and hexadecimal values. Specifically, I am able to convert values from binary to decimal (and vice-versa) but I am having trouble with the hexadecimal to binary conversion. Lets take single-precision floats for instance. When I read 4-bytes of data from a Stata .dta file which I know represent a missing value (i.e. the 4-bytes are represented by 00 00 00 7f in hexadecimal (on a LOHI system)) as, read DTA, my ($val), 4; $val = unpack("f", $val); This results in the following mappings: Stata value (bytes read) maps to (Perl variable $val) ------------------------ ---------------------------- . (0000007f) '1.70141183460469e+038' .a (0008007f) '1.70182721835338e+038' The reverse (decimal -> binary) conversion also works when I write a .dta file thusly, # de-reference object data my $val = $self->{DATA}{"$vlist[$k]"}{CELLS}[$n]; syswrite DTA, pack("f", $val), 4; So far, I am delighted, everything works as expected. The puzzling thing is when I try to write a missing value by 'packing' it from its hexadecimal representation, according to the following table (pasted from -help .dta-) V value HILO LOHI --------------------------------------------------------------- <snip> . +1.000000X+7f 7f000000 0000007f .a +1.001000X+7f 7f000800 0008007f .b +1.002000X+7f 7f001000 0010007f .z +1.01a000X+7f 7f00d000 00d0007f --------------------------------------------------------------- I don't get the expected results, e.g. if I try either syswrite DTA, pack("f", 0x0008007f), 4; or syswrite DTA, pack("f", 0x7f000800), 4; what gets written to DTA is F0070049 and 1000FE4E respectively, not the 0008007F I expected . Would anyone happen to know why I am having trouble with the hex -> binary conversion? Thanks in advance. Patrick Joly [email protected] [email protected] * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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