do i get my CON bonus at CL1

[Sky]

i just noticed something that, well, it's been bugging me for a while, but i just now saw it happen. but in the back of my mind i must have always known.

my brand new half-troll mage (best class in the game) has just dinged from CL1 to CL2, and his HP have jumped from 12 to 25.

WHAT ?

i have CON 15. i must assume that works at +1 hp per level, and i must also have 1d12 hp per level. How did i manage to gain 13 hp in one level, if my starting hp was 12?

Do we not get our CON bonus at CL1?

[Derakon]

At CON 15, you get an extra .5HP/level. At level 1, that means 12.5 HP, which rounds down to 12. A perfect roll on the hitdie at level 2 doubles that, to 25.

[Sky]

aha!

is that the reason why sometimes you can get down to 0 hp and still be alive?

[Pete Mack]

In most variants, 0HP is still enough. -1 is dead.

[Derakon]

Angband uses integer arithmetic for everything, so you can't actually have 12.5 HP. The .5 HP/level is represented in hundredths (so the value in the code is 50), and the non-integer portion of the calculation is discarded.

This is also why e.g. skill growths for classes are given in "growth per 10 levels" instead of "growth per level", and why the energy system for determining how quickly you get turns gives you a turn when you reach 100 energy, instead of when you reach 1 energy. The reason to do this is that when Angband was first written, many computers didn't have the ability to do floating-point calculations, because there was no Floating Point Unit (FPU) in their hardware. Sticking to integer-only made it possible to run Angband on a substantially larger number of computers. These days it's not so relevant though.