| 1 | import { BN } from '../bn/index.js';
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| 2 | import { u8aToBn, u8aToU8a } from '../u8a/index.js';
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| 3 | /**
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| 4 | * @name compactFromU8a
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| 5 | * @description Retrives the offset and encoded length from a compact-prefixed value
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| 6 | * @example
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| 7 | * <BR>
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| 8 | *
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| 9 | * ```javascript
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| 10 | * import { compactFromU8a } from '@polkadot/util';
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| 11 | *
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| 12 | * const [offset, length] = compactFromU8a(new Uint8Array([254, 255, 3, 0]));
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| 13 | *
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| 14 | * console.log('value offset=', offset, 'length=', length); // 4, 0xffff
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| 15 | * ```
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| 16 | */
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| 17 | export function compactFromU8a(input) {
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| 18 | const u8a = u8aToU8a(input);
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| 19 | // The u8a is manually converted here for 1, 2 & 4 lengths, it is 2x faster
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| 20 | // than doing an additional call to u8aToBn (as with variable length)
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| 21 | switch (u8a[0] & 0b11) {
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| 22 | case 0b00:
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| 23 | return [1, new BN(u8a[0] >>> 2)];
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| 24 | case 0b01:
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| 25 | return [2, new BN((u8a[0] + (u8a[1] << 8)) >>> 2)];
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| 26 | case 0b10:
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| 27 | // for the 3rd byte, we don't << 24 - since JS converts all bitwise operators to
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| 28 | // 32-bit, in the case where the top-most bit is set this yields a negative value
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| 29 | return [4, new BN((u8a[0] + (u8a[1] << 8) + (u8a[2] << 16) + (u8a[3] * 16777216)) >>> 2)];
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| 30 | // 0b11
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| 31 | default: {
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| 32 | // add 5 to shifted (4 for base length, 1 for this byte)
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| 33 | const offset = (u8a[0] >>> 2) + 5;
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| 34 | // we unroll the loop
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| 35 | switch (offset) {
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| 36 | // there still could be 4 bytes data, similar to 0b10 above (with offsets)
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| 37 | case 5:
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| 38 | // for the 3rd byte, we don't << 24 - since JS converts all bitwise operators to
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| 39 | // 32-bit, in the case where the top-most bit is set this yields a negative value
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| 40 | return [5, new BN(u8a[1] + (u8a[2] << 8) + (u8a[3] << 16) + (u8a[4] * 16777216))];
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| 41 | case 6:
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| 42 | return [6, new BN(u8a[1] + (u8a[2] << 8) + (u8a[3] << 16) + ((u8a[4] + (u8a[5] << 8)) * 16777216))];
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| 43 | // 6 bytes data is the maximum, 48 bits (56 would overflow)
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| 44 | case 7:
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| 45 | return [7, new BN(u8a[1] + (u8a[2] << 8) + (u8a[3] << 16) + ((u8a[4] + (u8a[5] << 8) + (u8a[6] << 16)) * 16777216))];
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| 46 | // for anything else, use the non-unrolled version
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| 47 | default:
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| 48 | return [offset, u8aToBn(u8a.subarray(1, offset))];
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| 49 | }
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| 50 | }
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| 51 | }
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| 52 | }
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| 53 | /**
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| 54 | * @name compactFromU8aLim
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| 55 | * @description A limited version of [[compactFromU8a]], accepting only Uint8Array inputs for values <= 48 bits
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| 56 | */
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| 57 | export function compactFromU8aLim(u8a) {
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| 58 | // The u8a is manually converted here for 1, 2 & 4 lengths, it is 2x faster
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| 59 | // than doing an additional call to u8aToBn (as with variable length)
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| 60 | switch (u8a[0] & 0b11) {
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| 61 | case 0b00:
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| 62 | return [1, u8a[0] >>> 2];
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| 63 | case 0b01:
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| 64 | return [2, (u8a[0] + (u8a[1] << 8)) >>> 2];
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| 65 | case 0b10:
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| 66 | // for the 3rd byte, we don't << 24 - since JS converts all bitwise operators to
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| 67 | // 32-bit, in the case where the top-most bit is set this yields a negative value
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| 68 | return [4, (u8a[0] + (u8a[1] << 8) + (u8a[2] << 16) + (u8a[3] * 16777216)) >>> 2];
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| 69 | // 0b11
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| 70 | default: {
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| 71 | // add 5 to shifted (4 for base length, 1 for this byte)
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| 72 | // we unroll the loop
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| 73 | switch ((u8a[0] >>> 2) + 5) {
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| 74 | // there still could be 4 bytes data, similar to 0b10 above (with offsets)
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| 75 | case 5:
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| 76 | return [5, u8a[1] + (u8a[2] << 8) + (u8a[3] << 16) + (u8a[4] * 16777216)];
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| 77 | case 6:
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| 78 | return [6, u8a[1] + (u8a[2] << 8) + (u8a[3] << 16) + ((u8a[4] + (u8a[5] << 8)) * 16777216)];
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| 79 | // 6 bytes data is the maximum, 48 bits (56 would overflow)
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| 80 | case 7:
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| 81 | return [7, u8a[1] + (u8a[2] << 8) + (u8a[3] << 16) + ((u8a[4] + (u8a[5] << 8) + (u8a[6] << 16)) * 16777216)];
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| 82 | // for anything else, we are above the actual MAX_SAFE_INTEGER - bail out
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| 83 | default:
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| 84 | throw new Error('Compact input is > Number.MAX_SAFE_INTEGER');
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| 85 | }
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| 86 | }
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| 87 | }
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| 88 | }
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