feat(#22): Gate B BDFT identity and rounding (TV-3, TV-10)

Pure units module: bdft = sqft × thickness_in (no /12), half-up rounding for sqft/bdft/price, length to nearest 1/8". Property checks for monotonicity in thickness and sqft. TDD: red evidence in test-results/tv3-tv10-red.txt, then minimum impl. Results: TV-3 | pass | test-results/tv3-tv10-green.txt TV-10 | pass | test-results/tv3-tv10-green.txt
2026-09-07 06:02:08 +00:00
parent 3c2f8871a8
commit 55d66b9644
6 changed files with 181 additions and 0 deletions
@@ -0,0 +1,39 @@
+import {
+  AREA_DECIMALS,
+  BDFT_DECIMALS,
+  INCH_STEP,
+  PRICE_DECIMALS,
+} from "./constants.js";
+
+/** Half-up at .5 (away from zero). */
+export function roundHalfUp(value: number, decimals: number): number {
+  if (!Number.isFinite(value)) {
+    return value;
+  }
+  const factor = 10 ** decimals;
+  const scaled = Math.abs(value) * factor;
+  const rounded = Math.floor(scaled + 0.5) / factor;
+  return value < 0 ? -rounded : rounded;
+}
+
+/** Nearest INCH_STEP (1/8"). */
+export function roundLengthIn(lengthIn: number): number {
+  return Math.round(lengthIn / INCH_STEP) * INCH_STEP;
+}
+
+export function roundSqft(sqft: number): number {
+  return roundHalfUp(sqft, AREA_DECIMALS);
+}
+
+export function roundBdft(bdft: number): number {
+  return roundHalfUp(bdft, BDFT_DECIMALS);
+}
+
+export function roundPrice(price: number): number {
+  return roundHalfUp(price, PRICE_DECIMALS);
+}
+
+/** bdft = sqft × thickness_in. No divide-by-12. */
+export function computeBdft(sqft: number, thicknessIn: number): number {
+  return roundBdft(sqft * thicknessIn);
+}