02d047fd5b93d96f159db2b8e95fc39450505159 refactor: add overflow-safe `CeilDiv` helper (Lőrinc)
Pull request description:
### Problem
The codebase has many open-coded ceiling-division expressions (for example `(x+y-1)/y`) scattered across files.
These are less readable, duplicate logic, and can be overflow-prone in edge cases.
### Fix
Introduce a small overflow-safe integer helper, `CeilDiv()`, and use it in existing **unsigned** callsites where the conversion is straightforward and noise-free.
### What this PR does
* Adds `CeilDiv()` to `src/util/overflow.h` for unsigned integral inputs.
* Keeps the precondition check `assert(divisor > 0)`.
* Replaces selected unsigned ceiling-division expressions with `CeilDiv(...)`.
* Adds focused unit tests in `src/test/util_tests.cpp` for the migrated patterns.
---
This is a pure refactor with no intended behavioral change.
Signed arithmetic callsites are intentionally left unchanged in this PR.
This PR changed a few more things originally but based on feedback reverted to the simplest cases only.
ACKs for top commit:
rustaceanrob:
ACK 02d047fd5b93d96f159db2b8e95fc39450505159
hodlinator:
ACK 02d047fd5b93d96f159db2b8e95fc39450505159
sedited:
ACK 02d047fd5b93d96f159db2b8e95fc39450505159
Tree-SHA512: b09336031f487e6ce289822e0ffeb8cfc8cfe8a2f4f3f49470748dfbd0a6cbab97498674cb8686dd2bd4ab6dd0b79cfdf2da00041fee12d109892e1bc5dde0ff
Introduce `TrySub(T&, U)` which subtracts an unsigned integral `U` from an unsigned integral `T`, returning `false` on underflow.
Use with `Assume(TrySub(...))` at coins cache accounting decrement sites so invariant violations fail immediately rather than silently wrapping.
Co-authored-by: MarcoFalke <*~=`'#}+{/-|&$^_@721217.xyz>
Co-authored-by: Pieter Wuille <pieter@wuille.net>
Introduce `CeilDiv()` for integral ceiling division without the typical `(dividend + divisor - 1) / divisor` overflow, asserting a non-zero divisor.
Replace existing ceiling-division expressions with `CeilDiv()` to centralize the preconditions.
Add unit tests covering return type deduction, max-value behavior, and divisor checks.
The helpers are used in the following commits to increase the safety of
conversions during cache size calculations.
Co-authored-by: Ryan Ofsky <ryan@ofsky.org>
Co-authored-by: stickies-v <stickies-v@protonmail.com>
