powerpc_nvram: Fix a bug in the adler32 checksum.
The Adler32 digest consists of two 16-bit words whose values are calculated modulo 65521 (largest prime < 2^16). To avoid two division instructions per byte, this version copies an optimization found in zlib which defers the modulus until close to the point that the intermediate sums can overflow 2^32. (zlib uses NMAX == 5552 for this, this version uses 5000) The bug is that in the deferred modulus case, the modulus was only applied to the high word (and twice at that) but not to the low word. The fix is to apply it to both words. Reviewed by: jhibbits Reported by: Miod Vallat <miod@openbsd.org> Differential Revision: https://reviews.freebsd.org/D36798
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@ -360,7 +360,7 @@ adler_checksum(uint8_t *data, int len)
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high = 0;
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high = 0;
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for (i = 0; i < len; i++) {
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for (i = 0; i < len; i++) {
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if ((i % 5000) == 0) {
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if ((i % 5000) == 0) {
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high %= 65521UL;
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low %= 65521UL;
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high %= 65521UL;
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high %= 65521UL;
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}
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}
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low += data[i];
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low += data[i];
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