I have the following example buffers and trying to extract some data from this.
<Buffer 38 31 aa 5e>
<Buffer 1c b2 4e 5f>
<Buffer c4 c0 28 60>
<Buffer 04 7a 52 60>
<Buffer 14 17 cd 60>
The data is in the format
Byte 1 - UTC nanosecond LS byte
Byte 2 - UTC nanosecond
Byte 3 - UTC nanosecond
Byte 4 - bits 0-5 UTC nanosecond upper 6 bits, 6-7 raw bits for debugging
I get bit shifting when I need whole bytes together but never needed to concatenate this with bits of a byte too. Any help?
You should be able to read the values as a single int and then use bitwise math to pull out the values.
// Read the value as little-endian since the least significant bytes are first.
var val = buf.readUInt32LE(0);
// Mask the last 2 bits out of the 32-bit value.
var nanoseconds = val & 0x3FFFFFFF;
// Mark just the final bits and convert to a boolean.
var bit6Set = !!(val & 0x40000000);
var bit7Set = !!(val & 0x80000000);
I have seen a better solution so I would like to share:
_getNode(bitIndex: number, id: Buffer) {
const byte = ~~(bitIndex / 8); // which byte to look at
const bit = bitIndex % 8; // which bit within the byte to look at
const idByte = id[byte]; // grab the byte from the buffer
if (idByte & Math.pow(2, (7 - bit))) { do something here } // check that the bit is set
}
It's just a little clearer / more concise. Notice how we use natural log2 pattern to our advantage to check if the bit is set.
