1 | /* adler32.c -- compute the Adler-32 checksum of a data stream |
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2 | * Copyright (C) 1995-2003 Mark Adler |
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3 | * For conditions of distribution and use, see copyright notice in zlib.h |
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4 | */ |
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5 | |
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6 | /* @(#) $Id: adler32.cc,v 1.1 2005/05/12 21:04:53 duns Exp $ */ |
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7 | |
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8 | #define ZLIB_INTERNAL |
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9 | #include "zlib.h" |
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10 | |
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11 | #define BASE 65521UL /* largest prime smaller than 65536 */ |
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12 | #define NMAX 5552 |
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13 | /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ |
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14 | |
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15 | #define DO1(buf,i) {s1 += buf[i]; s2 += s1;} |
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16 | #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); |
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17 | #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); |
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18 | #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); |
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19 | #define DO16(buf) DO8(buf,0); DO8(buf,8); |
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20 | |
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21 | #ifdef NO_DIVIDE |
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22 | # define MOD(a) \ |
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23 | do { \ |
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24 | if (a >= (BASE << 16)) a -= (BASE << 16); \ |
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25 | if (a >= (BASE << 15)) a -= (BASE << 15); \ |
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26 | if (a >= (BASE << 14)) a -= (BASE << 14); \ |
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27 | if (a >= (BASE << 13)) a -= (BASE << 13); \ |
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28 | if (a >= (BASE << 12)) a -= (BASE << 12); \ |
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29 | if (a >= (BASE << 11)) a -= (BASE << 11); \ |
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30 | if (a >= (BASE << 10)) a -= (BASE << 10); \ |
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31 | if (a >= (BASE << 9)) a -= (BASE << 9); \ |
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32 | if (a >= (BASE << 8)) a -= (BASE << 8); \ |
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33 | if (a >= (BASE << 7)) a -= (BASE << 7); \ |
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34 | if (a >= (BASE << 6)) a -= (BASE << 6); \ |
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35 | if (a >= (BASE << 5)) a -= (BASE << 5); \ |
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36 | if (a >= (BASE << 4)) a -= (BASE << 4); \ |
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37 | if (a >= (BASE << 3)) a -= (BASE << 3); \ |
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38 | if (a >= (BASE << 2)) a -= (BASE << 2); \ |
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39 | if (a >= (BASE << 1)) a -= (BASE << 1); \ |
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40 | if (a >= BASE) a -= BASE; \ |
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41 | } while (0) |
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42 | #else |
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43 | # define MOD(a) a %= BASE |
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44 | #endif |
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45 | |
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46 | /* ========================================================================= */ |
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47 | uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len) |
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48 | { |
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49 | unsigned long s1 = adler & 0xffff; |
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50 | unsigned long s2 = (adler >> 16) & 0xffff; |
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51 | int k; |
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52 | |
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53 | if (buf == Z_NULL) return 1L; |
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54 | |
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55 | while (len > 0) { |
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56 | k = len < NMAX ? (int)len : NMAX; |
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57 | len -= k; |
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58 | while (k >= 16) { |
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59 | DO16(buf); |
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60 | buf += 16; |
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61 | k -= 16; |
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62 | } |
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63 | if (k != 0) do { |
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64 | s1 += *buf++; |
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65 | s2 += s1; |
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66 | } while (--k); |
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67 | MOD(s1); |
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68 | MOD(s2); |
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69 | } |
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70 | return (s2 << 16) | s1; |
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71 | } |
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