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I'm trying to port a 1D perlin noise tutorial on C++

I'm trying to port a 1D perlin noise tutorial on C++ using SFMl lib : (tutorial link in javascript) https://codepen.io/Tobsta/post/procedural-generation-part-1-1d-perlin-noise
However this doesn't work, i don't get any error but this is what i get : https://i.imgur.com/2tAPhsH.png .
basically a straight line
And this is what i should get : https://i.imgur.com/GPnfsuK.png
Here's the ported code from the above link :
TerrainBorder constructor:
TerrainBorder::TerrainBorder(sf::RenderWindow &window) {
M = 4294967296;
A = 1664525;
C = 1;
std::random_device rd;
std::mt19937 rng(rd());
std::uniform_int_distribution<int> dist(0, M);
Z = floor(dist(rng) * M);
x = 0;
y = window.getSize().y / 2.0f;
amp = 100;
wl = 100;
fq = 1.0f / wl;
a = rand();
b = rand();
ar = sf::VertexArray(sf::Points);
}
Functions:
double TerrainBorder::rand()
{
Z = (A * Z + C) % M;
return Z / M - 0.5;
}
double TerrainBorder::interpolate(double pa, double pb , double px) {
double ft = px * PI,
f = (1 - cos(ft)) * 0.5;
return pa * (1 - f) + pb * f;
}
void TerrainBorder::drawPoints(sf::RenderWindow &window) {
while (x < window.getSize().x) {
if (static_cast<int> (x) % wl == 0) {
a = b;
b = rand();
y = window.getSize().y / 2 + a * amp;
} else {
y = window.getSize().y / 2 + interpolate(a, b, static_cast<int> (x)
% wl / wl) * amp;
}
ar.append(sf::Vertex(sf::Vector2f(x, y)));
x += 1;
}
}
Then i'm drawing the sf::VectorArray (which contains all the sf::Vertex in the game loop

i solved my problem ty for the answer anyway :)
I had to deal with types problems :p
I figured out that :
double c = x % 100 / 100;
std::cout << c << std::endl; // 0
!=
double c = x % 100;
std::cout << c / 100 << std::endl; // Some numbers depending on x
If it can help anyone in the future :)

C++ requires a careful choice for the types of the numeric variables, to avoid overflows and unexpected conversions.
The snippet shown in OP's question doesn't specify the types of M, A and Z, but uses a std::uniform_int_distribution of int, while M is initialized with a value that's out of the range of an int in most implementations.
It's also worth to be noted that the Standard Library already provides a std::linear_congruential_engine:
#include <iostream>
#include <random>
int main()
{
std::random_device rd;
std::mt19937 rng(rd());
// Calculate the first value
constexpr std::size_t M = 4294967296;
std::uniform_int_distribution<std::size_t> ui_dist(0, M);
std::size_t Z = ui_dist(rng);
// Initialize the engine
static std::linear_congruential_engine<std::size_t, 1664525, 1, M> lcg_dist(Z);
// Generate the values
for (int i = 0; i < 10; ++i)
{
Z = lcg_dist();
std::cout << Z / double(M) << '\n'; // <- To avoid an integer division
}
}

How to manipulate bits in Javascript?

Let's say I have a variable X = 4
How to create a number with a binary representation 1111 (ones with length X) using bitwise operators ( & | ~ << ^ ) and take a position and toggle the bit at that position to zero (0).
Example:
X = initial(4) // X should be : 1111
Y = solution(X, 2) // Y should be 1101
Z = solution(Y, 3) // Z should be 1001

Yes, you'd use Math.pow (or on modern browsers, the exponentiation operator, **) and the bitwise operators to do that.
function initial(digits) {
return Math.pow(2, digits) - 1;
}
function solution(value, bit) {
return value & ~(1 << (bit - 1)); // () around `bit - 1` aren't necessary,
// but I find it clearer
}
var X = initial(4); // X should be : 1111
console.log(X.toString(2));
var Y = solution(X, 2); // Y should be 1101
console.log(Y.toString(2));
var Z = solution(Y, 3); // Z should be 1001
console.log(Z.toString(2));
Or — doh! — comments on the question point out that you can create the initial number without Math.pow or exponentiation:
function initial(digits) {
return (1 << digits) - 1;
}
function solution(value, bit) {
return value & ~(1 << (bit - 1)); // () around `bit - 1` aren't necessary,
// but I find it clearer
}
var X = initial(4); // X should be : 1111
console.log(X.toString(2));
var Y = solution(X, 2); // Y should be 1101
console.log(Y.toString(2));
var Z = solution(Y, 3); // Z should be 1001
console.log(Z.toString(2));

Fast nearest power of 2 in JavaScript?

Is there any faster alternative to the following expression:
Math.pow(2,Math.floor(Math.log(x)/Math.log(2)))
That is, taking the closest (smaller) integer power of 2 of a double? I have such expression in a inner loop. I suspect it could be much faster, considering one could just take the mantissa from the IEEE 754 representation of the double.

Making use of ES6's Math.clz32(n) to count leading zeros of a 32-bit integer:
// Compute nearest lower power of 2 for n in [1, 2**31-1]:
function nearestPowerOf2(n) {
return 1 << 31 - Math.clz32(n);
}
// Examples:
console.log(nearestPowerOf2(9)); // 8
console.log(nearestPowerOf2(33)); // 32

Here's another alternative, with benchmarks. While both seems to be comparable, I like being able to floor or ceil.
function blpo2(x) {
x = x | (x >> 1);
x = x | (x >> 2);
x = x | (x >> 4);
x = x | (x >> 8);
x = x | (x >> 16);
x = x | (x >> 32);
return x - (x >> 1);
}
function pow2floor(v) {
var p = 1;
while (v >>= 1) {
p <<= 1;
}
return p;
}
function pow2ceil(v) {
var p = 2;
while (v >>= 1) {
p <<= 1;
}
return p;
}
function MATHpow2(v) {
return Math.pow(2, Math.floor(Math.log(v) / Math.log(2)))
}
function nearestPowerOf2(n) {
return 1 << 31 - Math.clz32(n);
}
function runner(fn, val) {
var res;
var st = new Date().getTime()
for (var i = 0; i < 100000000; i++) {
fn(val);
}
return (new Date().getTime() - st)
}
var source = 300000;
var a = runner(pow2floor, source);
console.log("\n--- pow2floor ---");
console.log(" result: " + pow2floor(source));
console.log(" time: " + a + " ms");
var b = runner(MATHpow2, source);
console.log("\n--- MATHpow2 ---");
console.log(" result: " + MATHpow2(source));
console.log(" time: " + b + " ms");
var b = runner(nearestPowerOf2, source);
console.log("\n--- nearestPowerOf2 ---");
console.log(" result: " + nearestPowerOf2(source));
console.log(" time: " + b + " ms");
var b = runner(blpo2, source);
console.log("\n--- blpo2 ---");
console.log(" result: " + blpo2(source));
console.log(" time: " + b + " ms");
// pow2floor: 1631 ms
// MATHpow2: 13942 ms
// nearestPowerOf2: 937 ms
// blpo2 : 919 ms **WINNER**

Here is also a branchless 32 bit version which is the fastest (9x) (on cellphones even more!) as of now.
It can also be scaled to 64 or 128 bits adding 1 or two lines:
x = x | (x >> 64);
x = x | (x >> 128);
on my computer:
2097152,blpo2: 118 ms **FASTEST**
2097152,nearestPowerOf2: 973 ms
2097152,pow2floor: 2033 ms
on my phone:
2097152,blpo2: 216 ms **FASTEST**
2097152,nearestPowerOf2: 1259 ms
2097152,pow2floor: 2904 ms
function blpo2(x) {
x = x | (x >> 1);
x = x | (x >> 2);
x = x | (x >> 4);
x = x | (x >> 8);
x = x | (x >> 16);
x = x | (x >> 32);
return x - (x >> 1);
}
function pow2floor(v) {
var p = 1;
while (v >>= 1) {
p <<= 1;
}
return p;
}
function nearestPowerOf2(n) {
return 1 << 31 - Math.clz32(n);
}
function runner(fn, val) {
var res;
var st = new Date().getTime()
for (var i = 0; i < 100000000; i++) {
res = fn(val);
}
dt = new Date().getTime() - st;
return res + "," + fn.name + ": " + dt + " ms"
}
var source = 3000000;
console.log(runner(blpo2, source), "**FASTEST**")
console.log(runner(nearestPowerOf2, source))
console.log(runner(pow2floor, source))

Unfortunately, you would need an equivalent of the C function frexp. The best I've been able to find is in JSFiddle, and its code uses Math.pow.
There are a couple of alternatives you could benchmark, using real data, along with your current attempt:
Starting at 1.0, multiply repeatedly by 2.0 until it is greater than or equal to the input, then multiply by 0.5 until it is less than or equal to the input. You would need special handling for values at the ends of the double range.
Store an ascending value array of all the exact powers of two in the double range, and do a binary search.
The first one is likely to be fastest if your data is typically close to 1.0. The second one requires up to 11 conditional branches.

Without ES6...
x=Math.floor(Math.random()*500000); //for example
nearestpowerof2=2**(x.toString(2).length-1);
console.log(x,">>>",nearestpowerof2);
In other words: the result is 2 to the power of the length of the binary representation of the number subtracted by 1.

And this is another.
function nP2(n) {
return 1 << Math.log2(n);
}
console.log(nP2(345367));
console.log(nP2(34536));
console.log(nP2(3453));
console.log(nP2(345));
console.log(nP2(34));

And another way (this one is slow but it's fun to code recursive ones):
function calc(n, c) {
c = c || 0;
n = n >> 1;
return (n > 0) ? calc(n, c + 1) : 2 ** c;
}
console.log(calc(345367));
console.log(calc(34536));
console.log(calc(3453));
console.log(calc(345));
console.log(calc(34));

Oh and I forgot the one-liner:
a=3764537465
console.log(2**~~Math.log2(a))
In other words, here we raise 2 to the power of the rounded logarithm in base 2 of the number. But alas, this is 140 times slower than the winner: blpo2 https://stackoverflow.com/a/74916422/236062

JavaScript CRC32

I'm looking for a modern JavaScript implementation of CRC32.
This implementation, which may have originated from here, and is now here, there and everywhere, is unacceptable because it's slow (500ms/MB), and depends on over 2KB of space delimited table, accessed using substr. Yuck!
There appears to be a few variations of CRC32, so I need to match this output:
mysql> SELECT CRC32('abcde');
> 2240272485
Function doesn't actually need to accept a string however, since I'm working with byte arrays.

Update
I added a helper function to create the CRCTable instead of having this enormous literal in the code. It could also be used to create the table once and save it in an object or variable and have the crc32 function use that (or as W3C's example, check for the existence and create if necessary). I also updated the jsPerf to compare using a CRCtable with the literal string, literal array, saved window variable and dynamic pointer (the example shown here).
var makeCRCTable = function(){
var c;
var crcTable = [];
for(var n =0; n < 256; n++){
c = n;
for(var k =0; k < 8; k++){
c = ((c&1) ? (0xEDB88320 ^ (c >>> 1)) : (c >>> 1));
}
crcTable[n] = c;
}
return crcTable;
}
var crc32 = function(str) {
var crcTable = window.crcTable || (window.crcTable = makeCRCTable());
var crc = 0 ^ (-1);
for (var i = 0; i < str.length; i++ ) {
crc = (crc >>> 8) ^ crcTable[(crc ^ str.charCodeAt(i)) & 0xFF];
}
return (crc ^ (-1)) >>> 0;
};
Here's a link to the performance difference: http://jsperf.com/js-crc32
Well here's my ameatur shot at this. I figured reading off an array is faster than substringing it.
Warning though, I forwent the use of the Utf8Encode function in these examples to simplify the tests. After all, these are just examples and pretty rough ones at that.

The code you link to do a substring and parses the result as number for each char. That's very inefficient.
I was able to make it 20 x faster with a simple optimization.
var a_table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
var b_table = a_table.split(' ').map(function(s){ return parseInt(s,16) });
function b_crc32 (str) {
var crc = -1;
for(var i=0, iTop=str.length; i<iTop; i++) {
crc = ( crc >>> 8 ) ^ b_table[( crc ^ str.charCodeAt( i ) ) & 0xFF];
}
return (crc ^ (-1)) >>> 0;
};
Performances comparison
JsBin to check it gives the same result

For ready-to-useness, here is a minified version of Alex's answer:
var crc32=function(r){for(var a,o=[],c=0;c<256;c++){a=c;for(var f=0;f<8;f++)a=1&a?3988292384^a>>>1:a>>>1;o[c]=a}for(var n=-1,t=0;t<r.length;t++)n=n>>>8^o[255&(n^r.charCodeAt(t))];return(-1^n)>>>0};
console.log(crc32('abc'));
console.log(crc32('abc').toString(16).toUpperCase()); // hex

I needed this ASAP so I wrote my own. Hope someone finds it useful.
196 bytes (After closure compiler). 16ms/MB
Edit: With improvements from everyone’s input.
var crc32 = (function()
{
var table = new Uint32Array(256);
// Pre-generate crc32 polynomial lookup table
// http://wiki.osdev.org/CRC32#Building_the_Lookup_Table
// ... Actually use Alex's because it generates the correct bit order
// so no need for the reversal function
for(var i=256; i--;)
{
var tmp = i;
for(var k=8; k--;)
{
tmp = tmp & 1 ? 3988292384 ^ tmp >>> 1 : tmp >>> 1;
}
table[i] = tmp;
}
// crc32b
// Example input : [97, 98, 99, 100, 101] (Uint8Array)
// Example output : 2240272485 (Uint32)
return function( data )
{
var crc = -1; // Begin with all bits set ( 0xffffffff )
for(var i=0, l=data.length; i<l; i++)
{
crc = crc >>> 8 ^ table[ crc & 255 ^ data[i] ];
}
return (crc ^ -1) >>> 0; // Apply binary NOT
};
})();

Based on #Denys Séguret's answer, I put together a crc32-adler implementation for a project of mine. It's a bit verbose, but is quite fast:
crc.js:
/* jslint node: true */
'use strict';
const CRC32_TABLE = new Int32Array([
0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f, 0xe963a535,
0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd,
0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 0x1adad47d,
0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,
0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac,
0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 0x2f6f7c87, 0x58684c11, 0xc1611dab,
0xb6662d3d, 0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb,
0x086d3d2d, 0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea,
0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65, 0x4db26158, 0x3ab551ce,
0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409,
0xce61e49f, 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a, 0xead54739,
0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344, 0x8708a3d2, 0x1e01f268,
0x6906c2fe, 0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0,
0x10da7a5a, 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8,
0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 0xcc0c7795, 0xbb0b4703,
0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7,
0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,
0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae,
0x0cb61b38, 0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777, 0x88085ae6,
0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, 0x4969474d,
0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5,
0x47b2cf7f, 0x30b5ffe9, 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
]);
exports.CRC32 = class CRC32 {
constructor() {
this.crc = -1;
}
update(input) {
input = Buffer.isBuffer(input) ? input : Buffer.from(input, 'binary');
return input.length > 10240 ? this.update_8(input) : this.update_4(input);
}
update_4(input) {
const len = input.length - 3;
let i = 0;
for(i = 0; i < len;) {
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
}
while(i < len + 3) {
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++] ) & 0xff ];
}
}
update_8(input) {
const len = input.length - 7;
let i = 0;
for(i = 0; i < len;) {
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++]) & 0xff ];
}
while(i < len + 7) {
this.crc = (this.crc >>> 8) ^ CRC32_TABLE[ (this.crc ^ input[i++] ) & 0xff ];
}
}
finalize() {
return (this.crc ^ (-1)) >>> 0;
}
};
You can then use this for streams and the like where data may come in chunks. Perform update on each chunk then finalize to get the result.
BTW: I found this to be a good source for checksum validation in addition to the built in *nix crc32 command.

Dystroy optimized, but still Alex is faster. Note that making the string from the document makes an unfair benchmark as the document grows as the testing progresses, since Alex is last he was the most data to process.
Table setup optimization is great but has debatable effect on the use time execution.
http://jsperf.com/alex-variations

Different output of binary operations on the same machine

Executing this JavaScript code in Safari
// expected output - array containing 32 bit words
b = "a";
var a = Array((b.length+3) >> 2);
for (var i = 0; i < b.length; i++) a[i>>2] |= (b.charCodeAt(i) << (24-(i & 3)*8));
and this (Objective-)C code in iOS Simulator
int array[((#"a".length + 3) >> 2)];
for (int i = 0; i < #"a".length; i++) {
int c = (int) [#"a" characterAtIndex:i];
array[i>>2] |= (c << (24-((i & 3)*8)));
}
gives me different output - consecutively (JavaScript) 1627389952 and (Objective-C) 1627748484.
Since the first four digits are always the same I think that the error is connected with precision but I cannot spot the issue.
EDIT
Sorry for this lack of attention and thank you very much (#Joni and all of you guys). You were right that the array in C code is fullfilled with some random values. I solved the issue setting all elements in the array to zero:
memset(array, 0, sizeof(array));
If anyone is curious the C code looks like this now:
int array[((#"a".length + 3) >> 2)];
memset(array, 0, sizeof(array));
for (int i = 0; i < #"a".length; i++) {
int c = (int) [#"a" characterAtIndex:i];
array[i>>2] |= (c << (24-((i & 3)*8)));
}

I don't know how Objective-c initializes arrays but in javascript
they are not initialized to anything (in fact, the indices don't even exist), so take care of that at least:
var b = "a";
var a = Array((b.length + 3) >> 2);
for( var i = 0, len = a.length; i < len; ++i ) {
a[i] = 0; //initialize a values to 0
}
for (var i = 0; i < b.length; i++) {
a[i >> 2] |= (b.charCodeAt(i) << (24 - (i & 3) * 8));
}
Secondly, this effectively should calculate 97 << 24, for which the correct
answer is 1627389952, so the Objective-C result is wrong. Probably because
the array values are not initialized to 0?

You are not setting the array to zeros in objective c, so it may have some random garbage to start with.