2 * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
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7 * without limitation the rights to use, copy, modify, merge, publish,
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9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
29 br_i15_decode_reduce(uint16_t *x,
30 const void *src, size_t len, const uint16_t *m)
32 uint32_t m_ebitlen, m_rbitlen;
34 const unsigned char *buf;
39 * Get the encoded bit length.
44 * Special case for an invalid (null) modulus.
52 * Clear the destination.
54 br_i15_zero(x, m_ebitlen);
57 * First decode directly as many bytes as possible. This requires
58 * computing the actual bit length.
60 m_rbitlen = m_ebitlen >> 4;
61 m_rbitlen = (m_ebitlen & 15) + (m_rbitlen << 4) - m_rbitlen;
62 mblen = (m_rbitlen + 7) >> 3;
65 br_i15_decode(x, src, len);
70 br_i15_decode(x, buf, k);
74 * Input remaining bytes, using 15-bit words.
85 br_i15_muladd_small(x, acc >> (acc_len - 15), m);
87 acc &= ~((uint32_t)-1 << acc_len);
92 * We may have some bits accumulated. We then perform a shift to
93 * be able to inject these bits as a full 15-bit word.
96 acc = (acc | (x[1] << acc_len)) & 0x7FFF;
97 br_i15_rshift(x, 15 - acc_len);
98 br_i15_muladd_small(x, acc, m);