Hi all
I am writing some python3 code where I am attempting to replicate the
printing of a lua-jit bytecode listing as done by a call to:
luajit -bl somefile.raw
I have it working correctly in most cases except for the handling of knums
(the constant float number values). I have 2 issues with knums:
1) My code produces slightly different values for some numbers. I assume
this is due to rounding errors, though surely it should be possible to
replicate how luajit is doing it so that I can get the exact same results?
The following examples show the luajit listing first, followed by my
listing:
0007 KNUM 6 0 ; 0.8
0007 KNUM 6 0 ; 0.8000000000009095
0066 KNUM 4 0 ; 0.4
0067 KNUM 5 1 ; 0.43
0068 KNUM 6 0 ; 0.4
0066 KNUM 4 0 ; 0.40000000000045477
0067 KNUM 5 1 ; 0.43
0068 KNUM 6 0 ; 0.40000000000045477
0076 KNUM 5 2 ; 0.3843137254902
0077 KNUM 6 3 ; 0.74117647058824
0076 KNUM 5 2 ; 0.38431372549065085
0077 KNUM 6 3 ; 0.7411764854893965
0075 KNUM 14 0 ; 0.05
0075 KNUM 14 0 ; 0.050000000000056846
2) The other issue I have is where my code generates vastly different
numbers. I can only assume that luajit is doing some special in these cases
that I am missing.
0053 TSETM 5 1 ; 1
0053 TSETM 5 1 ; 4503599627370497.0
0009 TSETM 1 0 ; 2
0009 TSETM 1 0 ; 4503599627370498.0
It may help to post the hex values of these here:
4503599627370497 == 0x00100000_00000001
4503599627370498 == 0x00100000_00000002
Also when loading these values from bytecode, the initial values loaded in
are:
hi=0x43300000, lo=0x00000001
hi=0x43300000, lo=0x00000002
I added some prints into the luajit sourcecode to confirm that I have
parsed these correctly from the bytecode. They are the same values that the
luajit source spits out via its calls to bcread_uleb128_33() and
bcread_uleb128() so I don't think my issue is at this point.
I then pack these two hi and lo values into consecutive 32bit unsigned
ints, and then unpack the resulting 64bits as a 64bit double. That is when
I get the results of:
hi=0x43300000, lo=0x00000001 --> 4503599627370497.0 (ie 0x00100000_00000001)
hi=0x43300000, lo=0x00000002 --> 4503599627370498.0 (ie 0x00100000_00000002)
I do this same pack/unpack conversion for other values which are either
correct off by the small rounding error mentioned in #1.
Can anyone help me fix these two issues? :)
thx
xor
