From c653c8cda8f49d3bbe07190a6477367290ff7f04 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Sun, 19 Apr 2020 16:28:10 -0400
Subject: Begin re-writing in Rust

---
 hilbert.c | 170 --------------------------------------------------------------
 1 file changed, 170 deletions(-)
 delete mode 100644 hilbert.c

(limited to 'hilbert.c')

diff --git a/hilbert.c b/hilbert.c
deleted file mode 100644
index 98cf247..0000000
--- a/hilbert.c
+++ /dev/null
@@ -1,170 +0,0 @@
-/*********************************************************************
- * kd-forest                                                         *
- * Copyright (C) 2015 Tavian Barnes <tavianator@tavianator.com>      *
- *                                                                   *
- * This program is free software. It comes without any warranty, to  *
- * the extent permitted by applicable law. You can redistribute it   *
- * and/or modify it under the terms of the Do What The Fuck You Want *
- * To Public License, Version 2, as published by Sam Hocevar. See    *
- * the COPYING file or http://www.wtfpl.net/ for more details.       *
- *********************************************************************/
-
-#include "hilbert.h"
-#include <stdint.h>
-
-// These algorithms are described in "Compact Hilbert Indices" by Chris Hamilton
-
-// Right rotation of x by b bits out of n
-static uint32_t
-ror(uint32_t x, unsigned int b, unsigned int n)
-{
-  uint32_t l = x & ((1 << b) - 1);
-  uint32_t r = x >> b;
-  return (l << (n - b)) | r;
-}
-
-// Left rotation of x by b bits out of n
-static uint32_t
-rol(uint32_t x, unsigned int b, unsigned int n)
-{
-  return ror(x, n - b, n);
-}
-
-// Binary reflected Gray code
-uint32_t
-gray_code(uint32_t i)
-{
-  return i ^ (i >> 1);
-}
-
-// e(i), the entry point for the ith sub-hypercube
-uint32_t
-entry_point(uint32_t i)
-{
-  if (i == 0) {
-    return 0;
-  } else {
-    return gray_code((i - 1) & ~1U);
-  }
-}
-
-// g(i), the inter sub-hypercube direction
-unsigned int
-inter_direction(uint32_t i)
-{
-  // g(i) counts the trailing set bits in i
-  unsigned int g = 0;
-  while (i & 1) {
-    ++g;
-    i >>= 1;
-  }
-  return g;
-}
-
-// d(i), the intra sub-hypercube direction
-unsigned int
-intra_direction(uint32_t i)
-{
-  if (i & 1) {
-    return inter_direction(i);
-  } else if (i > 0) {
-    return inter_direction(i - 1);
-  } else {
-    return 0;
-  }
-}
-
-// T transformation inverse
-uint32_t
-t_inverse(unsigned int dimensions, uint32_t e, unsigned int d, uint32_t a)
-{
-  return rol(a, d, dimensions) ^ e;
-}
-
-// GrayCodeRankInverse
-void
-gray_code_rank_inverse(unsigned int dimensions, uint32_t mu, uint32_t pi, unsigned int r, unsigned int free_bits, uint32_t *i, uint32_t *g)
-{
-  // *i is the inverse rank of r
-  // *g is gray_code(i)
-
-  *i = 0;
-  *g = 0;
-
-  for (unsigned int j = free_bits - 1, k = dimensions; k-- > 0;) {
-    if (mu & (1 << k)) {
-      *i |= ((r >> j) & 1) << k;
-      *g |= (*i ^ (*i >> 1)) & (1 << k);
-      --j;
-    } else {
-      *g |= pi & (1 << k);
-      *i |= (*g ^ (*i >> 1)) & (1 << k);
-    }
-  }
-}
-
-// ExtractMask
-void
-extract_mask(unsigned int dimensions, const unsigned int extents[], unsigned int i, uint32_t *mu, unsigned int *free_bits)
-{
-  // *mu is the mask
-  // *free_bits is popcount(*mu)
-
-  *mu = 0;
-  *free_bits = 0;
-
-  for (unsigned int j = dimensions; j-- > 0;) {
-    *mu <<= 1;
-
-    if (extents[j] > i) {
-      *mu |= 1;
-      *free_bits += 1;
-    }
-  }
-}
-
-// CompactHilbertIndexInverse
-void
-hilbert_point(unsigned int dimensions, const unsigned int extents[], uint32_t index, uint32_t point[])
-{
-  unsigned int max_extent = 0, total_extent = 0;
-  for (unsigned int i = 0; i < dimensions; ++i) {
-    if (extents[i] > max_extent) {
-      max_extent = extents[i];
-    }
-    total_extent += extents[i];
-    point[i] = 0;
-  }
-
-  uint32_t e = 0;
-  unsigned int k = 0;
-
-  // Next direction; we use d instead of d + 1 everywhere
-  unsigned int d = 1;
-
-  for (unsigned int i = max_extent; i-- > 0;) {
-    uint32_t mu;
-    unsigned int free_bits;
-    extract_mask(dimensions, extents, i, &mu, &free_bits);
-    mu = ror(mu, d, dimensions);
-
-    uint32_t pi = ror(e, d, dimensions) & ~mu;
-
-    unsigned int r = (index >> (total_extent - k - free_bits)) & ((1 << free_bits) - 1);
-
-    k += free_bits;
-
-    uint32_t w, l;
-    gray_code_rank_inverse(dimensions, mu, pi, r, free_bits, &w, &l);
-
-    l = t_inverse(dimensions, e, d, l);
-
-    for (unsigned int j = 0; j < 3; ++j) {
-      point[j] |= (l & 1) << i;
-      l >>= 1;
-    }
-
-    e = e ^ ror(entry_point(w), d, dimensions);
-    d = (d + intra_direction(w) + 1)%dimensions;
-  }
-}
-- 
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