Generally in Crawl, heavier weapons benefit more from strength than from dexterity. Strength weighting (abbreviated "str weight") is a game mechanic that determines relatively how much a character's strength and dexterity affect a given weapon's damage output.
A given str weight value can be viewed as a quotient expressed as a percentage; the "amount of effect" that strength has on a weapon, divided by the total amount of effect that strength and dexterity together have on it. So a str weight of 100% (such as with a giant club) implies that strength affects the weapon far more than dexterity does. Conversely, 0% (eg. quick blade) implies that strength has a very small effect on how well a weapon performs.
Almost all weapons fall somewhere in-between the two extremes. The weighted average of strength and dexterity affects both damage potential and to-hit, the former being affected more by strength and the latter being affected more by dexterity. Thus, note that that even 0% and 100% strength weightings don't imply that either stat has no effect: more dexterity always implies better to-hit and more strength always implies higher per-hit damage. A 50% str weight still implies that dexterity has a bigger effect than strength on to-hit, and conversely with strength and damage.
Formulas and source
In the source strength weight fractions are represented by integers from 0 to 10, representing 0% to 100% respectively. In the formulas below, W denotes strength weight as a fraction, ie. W=0.0 for quickblade and W=1.0 for giant club.
In the 0.12 source, melee damage is calculated a bit differently for monsters and player characters. Player damage potential is based on weapon base damage and, among other things, amplified by a stat value which is taken as a blend between the player's Str and Dex:
Melee damage blended stat = 0.5×Str + 0.5(W×Str + (1-W)Dex)
Stats are blended similiarly for to-hit but conversely to damage calculations, dexterity counts twice as heavily towards to-hit as strength does:
Melee to-hit blended stat = 0.5×Dex + 0.5(W×Str + (1-W)Dex)
The code for player-fired missile damage and to hit is even harder to decypher than for melee weapons. Strength and dexterity primarily affect the launcher "speed". "Speed" is a misnomer though: it means the amount of in-game time taken to fire a shot, not the rate at which shots are fired. Roughly:
Turns taken = ( launcher_base_attack_delay_percentile - player_skill×(W×Str + (W-1)×Dex)×4/25 ) / 100
- The concept of strength weighting was removed in 0.18.