wspatck.2da
The numbers there are for extra attacks depending on level. A 1 means +1 attack, a -1 means +1/2 attack (weird use of negative numbers). So it is why it goes weirdly from 0 to -1 to 1 to -2.
The original file by the way just goes up to -2 which is somehow wrong with AD&D rules I was told (hence the level 50 patch to rules that gets this modifier up to -3 which is 2.5 extrac attacks). I'm actually wondering where this file comes from though since it has weird jumps from -2 to -3 without going through 2...
In BG1 TotS we have:
2DA V1.0
0
LEVEL1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
0 0 0 0 0 0 0 -1 -1 -1 -1 -1 -1 1 1 1 1 1 1 1 1
1 0 0 0 0 0 0 -1 -1 -1 -1 -1 -1 1 1 1 1 1 1 1 1
2 -1 -1 -1 -1 -1 -1 1 1 1 1 1 1 -2 -2 -2 -2 -2 -2 -2 -2
3 -1 -1 -1 -1 -1 -1 1 1 1 1 1 1 -2 -2 -2 -2 -2 -2 -2 -2
4 -1 -1 -1 -1 -1 -1 1 1 1 1 1 1 -2 -2 -2 -2 -2 -2 -2 -2
5 -2 -2 -2 -2 -2 -2 2 2 2 2 2 2 -3 -3 -3 -3 -3 -3 -3 -3