List Fixed Window Center Anchor Tool

Description

Return start plus floor((width - 1)/2), start plus floor(width/2), and the geometric midpoint start + (width - 1)/2.

A list window uses a start and exclusive end or a center and radius. Boundary clamping, padding, and half-integer centers are separate conventions.

Return start plus floor((width - 1)/2), start plus floor(width/2), and the geometric midpoint start + (width - 1)/2.

Use List Fixed Window Center Anchor when you need an explicit window position or edge-padding budget.

Enter start, width. Use the units and conventions below.
Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
Read leftCenter, rightCenter, halfIndex. Use the output convention below.

Return start plus floor((width - 1)/2), start plus floor(width/2), and the geometric midpoint start + (width - 1)/2.^[1]

Input field	Meaning and units	Accepted input
start	Start	Required. Safe integer; minimum 0.
width	Width, count, or interval span under the stated formula.	Required. Safe integer; minimum 1.

json

{
  "input": {
    "start": 10,
    "width": 4
  },
  "output": {
    "leftCenter": 11,
    "rightCenter": 12,
    "halfIndex": 11.5
  }
}

Even widths have two center elements and a half-integer midpoint; no actual list bounds are supplied.
Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.

Inspect actual list bounds and choose whether to shift, truncate, or pad windows before extracting data.

List Run Split At Cursor
Return cursor as left and runLength minus cursor as right.
List Page Boundary Cursor Shift
Add pageSize times signed shiftPages to cursor.