Comment # 5
on bug 11042
from Guy Harris
RFC 6757, section 3.1.2:
http://tools.ietf.org/html/rfc6757#section-3.1.2
says:
Latitude Degrees: A 24-bit latitude degree value encoded as a two's
complement, fixed point number with 9 whole bits. Positive
degrees correspond to the Northern Hemisphere and negative degrees
correspond to the Southern Hemisphere. The value ranges from -90
to +90 degrees.
Longitude Degrees: A 24-bit longitude degree value encoded as a
two's complement, fixed point number with 9 whole bits. The value
ranges from -180 to +180 degrees.
In packet 24, the latitude, in degrees, is 0x0ad9d8.
0x0ad9d8, in binary, is 0000 1010 1101 1001 1101 1000.
If we put the binary point after the first 9 bits, to have 9 whole bits, that
would be 000010101.101100111011000.
000010101 is 21, and, for the fractional bits:
1 .5
0 .25
1 .125
1 .0625
0 .03125
0 .015625
1 .0078125
1 .00390625
1 .001953125
0 .0009765625
1 .00048828125
1 .000244140625
So that's 21+.701904296875 = 21.701904296875.
Please explain to me why a fixed-point binary value of 0x0ad9d8, with the
binary point after the first 9 bits, should have a value of 21.23 rather than
21.701904296875. What would the correct interpretation of RFC 6757, section
3.1.2, be, in order to yield that result rather than 21.701904296875?
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