# std/sum The exact sum of an `Array`, written in Vyrn. Adds `m` to the accumulator at the weight of exponent field `e`, negated when `negative`. `m` is a sum of up to 2048 values that share `e`: each is its fraction field, plus 2^52 when `e` is not 0. ## sum `fn`, at line 165. ```vyrn fn sum(xs: Array) -> Float64 ``` The true sum of `xs`, rounded once to the nearest `Float64` with ties to even. The result does not depend on the order of `xs`, on cancellation, or on an intermediate sum that would overflow: the largest finite value twice and its negation sum to the largest finite value. An infinity or a NaN follows IEEE: `+inf + -inf` is NaN, and a NaN anywhere makes the sum NaN. An exact zero is `+0.0`, and an empty array sums to `0.0`. A loop that adds with `+` keeps sequential rounding. An array of 512 values or more goes into slots by sign and exponent, with no rounding. Four tables of 4096 slots take every fourth value in turn, so a run of equal exponents does not wait on one slot. A slot moves into a 2304-bit accumulator before it can overflow. Shorter arrays go straight to the accumulator. --- From https://vyrn-lang.github.io/docs/std/sum.html — generated by `site/export.vyrn` from the Vyrn repository.