''From a post in news:comp.lang.tcl :''

Floating point values are usually transferred in IEEE format. I have
written the following code to read an IEEE float value for the case
that your machine doesn't use IEEE natively.
 proc IEEE2float {data byteorder} {
    if {$byteorder == 0} {
        set code [binary scan $data cccc se1 e2f1 f2 f3]
    } else {
        set code [binary scan $data cccc f3 f2 e2f1 se1]
    }
    
    set se1  [expr {($se1 + 0x100) % 0x100}]
    set e2f1 [expr {($e2f1 + 0x100) % 0x100}]
    set f2   [expr {($f2 + 0x100) % 0x100}]
    set f3   [expr {($f3 + 0x100) % 0x100}]
    
    set sign [expr {$se1 >> 7}]
    set exponent [expr {(($se1 & 0x7f) << 1 | ($e2f1 >> 7))}]
    set f1 [expr {$e2f1 & 0x7f}]
    
    set fraction [expr {double($f1)*0.0078125 + \
            double($f2)*3.0517578125e-05 + \
            double($f3)*1.19209289550781e-07}]
    
    set res [expr {($sign ? -1. : 1.) * \
            pow(2.,double($exponent-127)) * \
            (1. + $fraction)}]
    return $res
 }

It expects a binary buffer containing an IEEE number and the byte order
the number is in (0 for big-endian and 1 for little-endian).

3fa22435 yields 1.2667299509 (big-endian) or 6.1330860035e-07 (little).
 
 + Frank Pilhofer                        fp@informatik.uni-frankfurt.de   +
 |                                      http://www.uni-frankfurt.de/~fp/
----
Also see [1750A to Float Conversion] for converting to and from a MIL-STD-1750A 32-bit floating number.

[Michael Jacobson] ~ jakeforce@home.com

----
[CL] intends to make time to
demonstrate how the constants above introduce small imprecisions around the twelfth
decimal place.
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[Category Binary Data]