word-list-sum

A list sum over wrapping or saturating words is exact; the store applies the word's policy.

Syntax: <list<wrapping<W>>>.sum()

Category#

arithmetic

Related#

• wrapping
• saturating
• list

Examples#

radix/corpus/operatores/word-list-sum.fab (canonical · operator-group)#

A list sum over wrapping or saturating words is exact; the store applies the word's policy.

# =============================================================================
# word-list-sum — a list sum over words is exact until the store.
# =============================================================================
#
# What this teaches:
#   • "Math happens in the ether, and only at the store do we apply any of the
#     boundary conditions." `sum()` over `wrapping<u8>` or `saturating<u8>`
#     elements adds exactly, so `200 + 100` is `300` when it is printed.
#   • The store applies the slot's policy once: a `wrapping<u8>` cell holds
#     `300 mod 256 = 44`, a `saturating<u8>` cell holds the clamp `255`.
#   • Nothing wraps or clamps per element or per partial sum.
#
# Common mistakes:
#   • Expecting `print ws.sum()` to show `44` or `255` — the unstored total is
#     the exact `300`.
#   • Expecting a wrapping or saturating partial sum — the policy is applied
#     once, at the store.
#
# See also: wrapping, saturating, list
# =============================================================================

# word-list-sum — exact word sum, policy at the store
#
# EXPECTED OUTPUT:
#   300
#   44
#   300
#   255
#
# BACKEND: runner-pinned stdout (word-list-sum.expected).

main {
    let list<wrapping<u8>> ws ← [200, 100]
    print ws.sum()
    let wrapping<u8> wrapped ← ws.sum()
    print wrapped
    let list<saturating<u8>> ss ← [200, 100]
    print ss.sum()
    let saturating<u8> clamped ← ss.sum()
    print clamped
}

Expected output:

300
44
300
255