Monday, March 11, 2013

Hexadecimal literals in GNU R

Recently I have used hexadecimal numbers in GNU R. The way they are parsed surprised me and is inconsistent with Java. As R Language Definition pdf only briefly mentions hexadecimal numbers here is what I have found.

First I have checked the following code:

0x11
# 17
0x1.1
# 17

I seemed that GNU R drops the decimal point. So I have checked notation with exponent being power of 2 (as in Java):

0x1.1p0
# 1.0625
0x1.1p4
# 17

Now decimal point is correctly taken into account so I have checked further.

In the notation without exponent part GNU R just discards decimal points as in this example:

0x111
# 273
0x1.1.1
# 273
0x....1....1....1
# 273

However, in notation with exponent last decimal point is taken into consideration and all earlier decimal points are ignored:

0x11.1p0
# 17.0625
0x1.1.1p0
# 17.0625
0x....1....1....1p0
# 17.0625

In summary - handling of hexadecimal literals in GNU R is nonstandard and at least for me - unexpected.

1 comment:

  1. Post to R-devel - this looks like a parser bug and if it is then it would be nice if it's fixed in time for the R 3.0.0 release.

    /Henrik Bengtsson

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