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/* HuffEnc.c -- functions for Huffman encoding
2023-09-07 : Igor Pavlov : Public domain */
#include "Precomp.h"
#include "HuffEnc.h"
#include "Sort.h"
#define kMaxLen 16
#define NUM_BITS 10
#define MASK ((1u << NUM_BITS) - 1)
#define NUM_COUNTERS 64
#define HUFFMAN_SPEED_OPT
void Huffman_Generate(const UInt32 *freqs, UInt32 *p, Byte *lens, UInt32 numSymbols, UInt32 maxLen)
{
UInt32 num = 0;
/* if (maxLen > 10) maxLen = 10; */
{
UInt32 i;
#ifdef HUFFMAN_SPEED_OPT
UInt32 counters[NUM_COUNTERS];
for (i = 0; i < NUM_COUNTERS; i++)
counters[i] = 0;
for (i = 0; i < numSymbols; i++)
{
UInt32 freq = freqs[i];
counters[(freq < NUM_COUNTERS - 1) ? freq : NUM_COUNTERS - 1]++;
}
for (i = 1; i < NUM_COUNTERS; i++)
{
UInt32 temp = counters[i];
counters[i] = num;
num += temp;
}
for (i = 0; i < numSymbols; i++)
{
UInt32 freq = freqs[i];
if (freq == 0)
lens[i] = 0;
else
p[counters[((freq < NUM_COUNTERS - 1) ? freq : NUM_COUNTERS - 1)]++] = i | (freq << NUM_BITS);
}
counters[0] = 0;
HeapSort(p + counters[NUM_COUNTERS - 2], counters[NUM_COUNTERS - 1] - counters[NUM_COUNTERS - 2]);
#else
for (i = 0; i < numSymbols; i++)
{
UInt32 freq = freqs[i];
if (freq == 0)
lens[i] = 0;
else
p[num++] = i | (freq << NUM_BITS);
}
HeapSort(p, num);
#endif
}
if (num < 2)
{
unsigned minCode = 0;
unsigned maxCode = 1;
if (num == 1)
{
maxCode = (unsigned)p[0] & MASK;
if (maxCode == 0)
maxCode++;
}
p[minCode] = 0;
p[maxCode] = 1;
lens[minCode] = lens[maxCode] = 1;
return;
}
{
UInt32 b, e, i;
i = b = e = 0;
do
{
UInt32 n, m, freq;
n = (i != num && (b == e || (p[i] >> NUM_BITS) <= (p[b] >> NUM_BITS))) ? i++ : b++;
freq = (p[n] & ~MASK);
p[n] = (p[n] & MASK) | (e << NUM_BITS);
m = (i != num && (b == e || (p[i] >> NUM_BITS) <= (p[b] >> NUM_BITS))) ? i++ : b++;
freq += (p[m] & ~MASK);
p[m] = (p[m] & MASK) | (e << NUM_BITS);
p[e] = (p[e] & MASK) | freq;
e++;
}
while (num - e > 1);
{
UInt32 lenCounters[kMaxLen + 1];
for (i = 0; i <= kMaxLen; i++)
lenCounters[i] = 0;
p[--e] &= MASK;
lenCounters[1] = 2;
while (e != 0)
{
UInt32 len = (p[p[--e] >> NUM_BITS] >> NUM_BITS) + 1;
p[e] = (p[e] & MASK) | (len << NUM_BITS);
if (len >= maxLen)
for (len = maxLen - 1; lenCounters[len] == 0; len--);
lenCounters[len]--;
lenCounters[(size_t)len + 1] += 2;
}
{
UInt32 len;
i = 0;
for (len = maxLen; len != 0; len--)
{
UInt32 k;
for (k = lenCounters[len]; k != 0; k--)
lens[p[i++] & MASK] = (Byte)len;
}
}
{
UInt32 nextCodes[kMaxLen + 1];
{
UInt32 code = 0;
UInt32 len;
for (len = 1; len <= kMaxLen; len++)
nextCodes[len] = code = (code + lenCounters[(size_t)len - 1]) << 1;
}
/* if (code + lenCounters[kMaxLen] - 1 != (1 << kMaxLen) - 1) throw 1; */
{
UInt32 k;
for (k = 0; k < numSymbols; k++)
p[k] = nextCodes[lens[k]]++;
}
}
}
}
}
#undef kMaxLen
#undef NUM_BITS
#undef MASK
#undef NUM_COUNTERS
#undef HUFFMAN_SPEED_OPT
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