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Add bufrange to support reusing buffers #25

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Add bufrange to support reusing buffers #25

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11 changes: 8 additions & 3 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -32,7 +32,7 @@ var CRC32 = require("crc-32");
Using NodeJS or a bundler with `import`:

```js
import { bstr, buf, str } from "crc-32";
import { bstr, buf, bufrange, str } from "crc-32";
```

In the browser, the `crc32.js` script can be loaded directly:
Expand All @@ -59,7 +59,7 @@ var CRC32C = require("crc-32/crc32c");
Using NodeJS or a bundler with `import`:

```js
import { bstr, buf, str } from "crc-32/crc32c";
import { bstr, buf, bufrange, str } from "crc-32/crc32c";
```

In the browser, the `crc32c.js` script can be loaded directly:
Expand All @@ -83,6 +83,11 @@ optional second argument representing the starting "seed" (for rolling CRC).
- `CRC32.buf(byte array or buffer[, seed])` assumes the argument is a sequence
of 8-bit unsigned integers (nodejs `Buffer`, `Uint8Array` or array of bytes).

- `CRC32.bufrange(byte array or buffer, start, end, [, seed])` assumes the first argument is a sequence
of 8-bit unsigned integers (nodejs `Buffer`, `Uint8Array` or array of bytes), the second argument marks
the start index (inclusive) and the third argument marks the end index (exclusive) of the range to read
from the buffer.

- `CRC32.bstr(binary string[, seed])` assumes the argument is a binary string
where byte `i` is the low byte of the UCS-2 char: `str.charCodeAt(i) & 0xFF`

Expand All @@ -96,6 +101,7 @@ For example:
CRC32.str("SheetJS") // -1647298270
CRC32.bstr("SheetJS") // -1647298270
CRC32.buf([ 83, 104, 101, 101, 116, 74, 83 ]) // -1647298270
CRC32.bufrange([ 83, 104, 101, 101, 74 ], 1, 2) // -1826163454

crc32 = CRC32.buf([83, 104]) // -1826163454 "Sh"
crc32 = CRC32.str("eet", crc32) // 1191034598 "Sheet"
Expand All @@ -108,7 +114,6 @@ CRC32.bstr("JS", crc32) // -1647298270 "SheetJS"
// var CRC32C = require('crc-32/crc32c'); // uncomment this line if in node
CRC32C.str("SheetJS") // -284764294
CRC32C.bstr("SheetJS") // -284764294
CRC32C.buf([ 83, 104, 101, 101, 116, 74, 83 ]) // -284764294

crc32c = CRC32C.buf([83, 104]) // -297065629 "Sh"
crc32c = CRC32C.str("eet", crc32c) // 1241364256 "Sheet"
Expand Down
8 changes: 7 additions & 1 deletion crc32.js
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Expand Up @@ -68,7 +68,11 @@ function crc32_bstr(bstr, seed) {
}

function crc32_buf(B, seed) {
var C = seed ^ -1, L = B.length - 15, i = 0;
return crc32_bufrange(B, 0, B.length, seed);
}

function crc32_bufrange(B, start, end, seed) {
var C = seed ^ -1, L = end - start - 15, i = 0;
for(; i < L;) C =
Tf[B[i++] ^ (C & 255)] ^
Te[B[i++] ^ ((C >> 8) & 255)] ^
Expand Down Expand Up @@ -111,5 +115,7 @@ CRC32.bstr = crc32_bstr;
// $FlowIgnore
CRC32.buf = crc32_buf;
// $FlowIgnore
CRC32.bufrange = crc32_bufrange;
// $FlowIgnore
CRC32.str = crc32_str;
}));