137 lines
4.1 KiB
C++
137 lines
4.1 KiB
C++
#ifndef THREE_PASS_XB_H
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#define THREE_PASS_XB_H
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/* Basically like threepass.h but but fewer bits - only for thiersort3! */
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/* How the 28-30 bits gets separated? This is chosen because I saw that: */
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/* - in float trickery I saw at around 4 billion the buckets change around 200 million */
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/* - Which is smaller than 1/2 or 1/4 or 1/8 or 1/16 of it because 16*200 mil = 3.2 bill 28 bit is needed */
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/* - This means those bits in numbers DO get used when we are running as internal sort of thier3 */
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/* - But the numbers high bits (29..32th bits) stay the same inside each bucket so we spare it! */
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/* - If you know your data does not have all the range of 32 bits you can #define these by #define CUSTOM_TPBX_BITS */
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#ifndef CUSTOM_TPBX_BITS
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#define TPBX1 10 // top
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#define TPBX2 9 // mid
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#define TPBX3 9 // bottom
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#endif /* CUSTOM_TPBX_BITS */
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static inline constexpr uint32_t min3u32_xb(uint32_t a, uint32_t b, uint32_t c) noexcept {
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return (a <= b) ?
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((a <= c) ? a : c) :
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((b <= c) ? b : c);
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}
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/**
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* Simple three-pass (ok: 3 + 1) bottom-up internal radix sort writter for thiersort3
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*
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* @param a The array to sort - will be changed too!
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* @param buf Result array with the same size - result will be here
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* @param n The number of elements
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*/
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static inline void threepass_xb(uint32_t *a, uint32_t *buf, int n) noexcept {
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assert(buf != NULL);
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constexpr int shr1 = TPBX3 + TPBX2;
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constexpr int shr2 = TPBX3;
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constexpr int shr3 = 0;
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constexpr int mask1 = (1 << TPBX1) - 1;
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constexpr int mask2 = (1 << TPBX2) - 1;
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constexpr int mask3 = (1 << TPBX3) - 1;
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/* helper buffers. */
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int sz = n * sizeof(a[0]);
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static thread_local uint32_t bucket1[1 << TPBX1];
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memset(bucket1, 0, (1 << TPBX1) * sizeof(uint32_t));
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static thread_local uint32_t bucket2[1 << TPBX2];
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memset(bucket2, 0, (1 << TPBX2) * sizeof(uint32_t));
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static thread_local uint32_t bucket3[1 << TPBX3];
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memset(bucket3, 0, (1 << TPBX3) * sizeof(uint32_t));
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/* Count occurences (can count together with good ILP) */
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#pragma GCC unroll 64
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for(uint32_t i = 0; i < n; ++i) {
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++bucket1[(a[i] >> shr1) & mask1];
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++bucket2[(a[i] >> shr2) & mask2];
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++bucket3[(a[i] >> shr3) & mask3];
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}
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/* Count prefix sums - try as much ILP as possible because bigger arrays than usual! */
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uint32_t prev1 = 0;
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uint32_t prev2 = 0;
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uint32_t prev3 = 0;
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uint32_t common = min3u32_xb(
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(1 << TPBX1),
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(1 << TPBX2),
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(1 << TPBX3)
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);
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int i = 0;
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#pragma GCC unroll 8
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for (; i < common; ++i) {
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bucket1[i] += prev1;
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prev1 = bucket1[i];
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bucket2[i] += prev2;
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prev2 = bucket2[i];
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bucket3[i] += prev3;
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prev3 = bucket3[i];
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}
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/* Do remaining 1 */
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for (int j = i; j < (1 << TPBX1); ++j) {
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bucket1[j] += prev1;
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prev1 = bucket1[j];
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}
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/* Do remaining 2 */
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for (int j = i; j< (1 << TPBX2); ++j) {
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bucket2[j] += prev2;
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prev2 = bucket2[j];
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}
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/* Do remaining 3 */
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for (int j = i; j < (1 << TPBX3); ++j) {
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bucket3[j] += prev3;
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prev3 = bucket3[j];
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}
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// Bottom digit a->buf
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// right-to-left to ensure already sorted digits order we keep for iterations
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#pragma GCC unroll 48
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for(uint32_t i = n; i > 0; --i) {
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// Prefetch caches
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//__builtin_prefetch(&a[i-8]);
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// Get num and its new offset / location
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auto num = a[i - 1];
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auto bkeyni = (num >> shr3) & mask3;
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auto offset = --bucket3[bkeyni];
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// Add to the proper target location
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buf[offset] = num;
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}
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// Mid digit buf->a
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// right-to-left to ensure already sorted digits order we keep for iterations
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#pragma GCC unroll 48
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for(uint32_t i = n; i > 0; --i) {
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// Prefetch caches
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//__builtin_prefetch(&buf[i-8]);
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// Get num and its new offset / location
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auto num = buf[i - 1];
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auto bkeyni = (num >> shr2) & mask2;
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auto offset = --bucket2[bkeyni];
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// Add to the proper target location
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a[offset] = num;
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}
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// Top digit a->buf
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// right-to-left to ensure already sorted digits order we keep for iterations
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#pragma GCC unroll 48
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for(uint32_t i = n; i > 0; --i) {
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// Prefetch caches
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// __builtin_prefetch(&a[i-16]);
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// Get num and its new offset / location
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auto num = a[i - 1];
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auto bkeyni = (num >> shr1) & mask1;
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auto offset = --bucket1[bkeyni];
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// Add to the proper target location
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buf[offset] = num;
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}
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}
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#endif /* THREE_PASS_XB_H */
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