Copy page

Developer Guide

Division and periodicity

PostgreSQL-faithful scale

div(a, b) without an explicit scale uses PostgreSQL's own select_div_scale rule — max(16 - 4·qweight, scale_a, scale_b) where qweight is the weight of the quotient's integer part. The output is digit-for-digit identical to numeric division on the database:

PostgreSQL	div() result
1/3	0.33333333333333333333
10/4	2.5000000000000000
100/3	33.3333333333333333

pgDivScale(a, b) exposes the computed scale if you need it for pre-validation.

Fixed scale override

Code
div(total, 8, 2);                               // force scale 2 (HALF_UP)
div(a, b, { scale: 6, rounding: "HALF_EVEN" }); // force scale + rounding mode

The isPeriodic flag

isPeriodic(d) is true when the last division produced a non-terminating expansion that was truncated (e.g. 1/3). The flag propagates through operations — a downstream computation on a periodic operand stays flagged, so callers can decide to round for display while keeping the precise value internally:

Code
const third = div(1, 3);
isPeriodic(third);              // true
isPeriodic(mul(third, 2));      // true — propagates
isPeriodic(add(third, "1"));    // true — propagates
isPeriodic(div(4, 2));          // false