31:[] 2f:{"title":"H3 Index Bit Layout","cells":[{"id":0,"value":"md`# H3 Index Bit Layout\n\nH3 indexes are 64-bit integers, usually serialized to hexidecimal strings. The [bit layout of the index](https://h3geo.org/docs/core-library/h3indexing) offers a relatively compact structure for storing information about a given index and defining its geographic position, potentially down to the square meter.\n`","pinned":false,"hidden":false,"mode":"ojs"},{"id":5,"value":"viewof inputText = {\n const defaultIndex = '85283473fffffff';\n const fromUrl = decodeURIComponent(window.location.hash.slice(1));\n return html``\n};","pinned":false,"hidden":false,"mode":"ojs"},{"id":127,"value":"{\n const [lower, upper] = h3IndexToSplitLong(inputText);\n // the weird dance here is because Number#toString doesn't deal properly\n // with the highest bit of a 32-bit int\n // const upperTop = String(upper >>> 31);\n // const lowerTop = String(lower >>> 31);\n const zeroFill = new Array(32).fill('0').join('');\n const upperStr = upper.toString(2);\n const lowerStr = lower.toString(2);\n \n const bits = (\n zeroFill.slice(upperStr.length) + upperStr + \n zeroFill.slice(lowerStr.length) + lowerStr\n ).split('');\n \n const selected = new Array(bits.length);\n for (const {start, bits} of selectedChunks) {\n for (let bit = start; bit < start + bits; bit++) {\n selected[bit] = true;\n }\n }\n \n return html`\n

\n ${\n bits.map((digit, i) => html`\n ${digit}\n `)\n }\n

\n `;\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":95,"value":"viewof selectedChunks = Table(chunks, {\n rows: chunks.length + 1, \n required: false, \n width: 'auto',\n align: {\n start: 'left',\n bits: 'left'\n },\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":178,"value":"md`### Notes\n- The Index Mode indicates whether the index represents a grid cell or another entity (the library currently also supports directed edges and vertices).\n- The resolution digits indicate which child of the previous resolution is indexed. The base cell *is* the res 0 index, so we don't need a Res 0 digit.\n- Trailing resolution digits set to 7 are unused.\n`","pinned":false,"hidden":false,"mode":"ojs"},{"id":171,"value":"md`\n---\n### Utils`","pinned":false,"hidden":false,"mode":"ojs"},{"id":19,"value":"chunks = {\n const h3Index = inputText;\n const [lower, upper] = h3IndexToSplitLong(h3Index);\n const mode = getMode(lower, upper)\n const baseCell = getBaseCell(lower, upper);\n // assert(baseCell === h3.h3GetBaseCell(h3Index));\n const resolution = getRes(lower, upper);\n // assert(resolution === h3.h3GetResolution(h3Index));\n const reserved = getReserved(lower, upper);\n \n const chunks = [\n {start: 0, bits: 1, type: 'Reserved', value: 0},\n {start: 1, bits: 4, type: 'Index Mode', value: mode},\n {start: 5, bits: 3, type: 'Mode-Dependent', value: reserved},\n {start: 8, bits: 4, type: 'Resolution', value: resolution},\n {start: 12, bits: 7, type: 'Base Cell', value: baseCell},\n ];\n \n const digits = [];\n for (let i = 1; i < 16; i++) {\n chunks.push({\n start: 19 + (i - 1) * 3,\n bits: 3,\n type: `Res ${i} digit`,\n value: getIndexDigit(lower, upper, i)\n })\n }\n \n return chunks;\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":65,"value":"function getIndexDigit(lower, upper, res) {\n const H3_PER_DIGIT_OFFSET = 3;\n const H3_DIGIT_MASK = 7;\n const MAX_H3_RES = 15;\n const UPPER_RES_OFFSET = 11;\n const UPPER_SPLIT_RES = 1;\n const LOWER_SPLIT_RES = H3_PER_DIGIT_OFFSET - UPPER_SPLIT_RES;\n // res < 5 is in the upper bits, with a one-bit offset\n if (res < 5) {\n return (upper >> UPPER_SPLIT_RES + (\n (MAX_H3_RES - UPPER_RES_OFFSET - res) * H3_PER_DIGIT_OFFSET\n )) & H3_DIGIT_MASK;\n }\n // res > 5 is in the lower bits\n if (res > 5) {\n return (lower >> ((MAX_H3_RES - res) * H3_PER_DIGIT_OFFSET)) & H3_DIGIT_MASK;\n }\n // res 5 is annoyingly split across upper and lower\n return ((upper & 1) << 2) + (lower >>> 30); \n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":25,"value":"function getMode(lower, upper) {\n const OFFSET = 59 - 32;\n const MASK = 15 << OFFSET;\n return (upper & MASK) >> OFFSET;\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":39,"value":"function getBaseCell(lower, upper) {\n const OFFSET = 45 - 32;\n const MASK = 127 << OFFSET;\n return (upper & MASK) >> OFFSET;\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":48,"value":"function getRes(lower, upper) {\n const OFFSET = 52 - 32;\n const MASK = 15 << OFFSET;\n return (upper & MASK) >> OFFSET;\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":56,"value":"function getReserved(lower, upper) {\n const OFFSET = 56 - 32;\n const MASK = 7 << OFFSET;\n return (upper & MASK) >> OFFSET;\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":15,"value":"function h3IndexToSplitLong(inputText) {\n const h3Index = inputText.trim();\n if (!h3.h3IsValid(h3Index) && !h3.h3UnidirectionalEdgeIsValid(h3Index)) {\n throw new Error('Please enter a valid H3 index');\n }\n const upper = parseInt(h3Index.substring(0, h3Index.length - 8), 16);\n const lower = parseInt(h3Index.substring(h3Index.length - 8), 16);\n return [lower, upper];\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":42,"value":"function assert(assertion, msg) {\n if (!assertion) {\n throw new Error(msg || 'Assertion failed')\n }\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":104,"value":"md`\n---\n### Dependencies`","pinned":false,"hidden":false,"mode":"ojs"},{"id":101,"value":"import {Table} from \"@observablehq/inputs\"","pinned":false,"hidden":false,"mode":"ojs"},{"id":20,"value":"h3 = require('h3-js@3.7.2')","pinned":false,"hidden":false,"mode":"ojs"}],"files":"$W31","stdlib":"1","titling":"auto"}