thodg/libgit2/src/util/tsort.c

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• Hash : c3b7ace9
  Author :
  Date : 2021-11-14T16:43:53
  

  refactor: make util an object library Instead of simply including the utility files directly, make them a cmake object library for easy reusability between other projects within libgit2. Now the top-level `src` is responsible for platform selection, while the next-level `libgit2` and `util` configurations are responsible for identifying what objects they include.

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• src/util/tsort.c

• /*
   * Copyright (C) the libgit2 contributors. All rights reserved.
   *
   * This file is part of libgit2, distributed under the GNU GPL v2 with
   * a Linking Exception. For full terms see the included COPYING file.
   */
  
  #include "git2_util.h"
  
  /**
   * An array-of-pointers implementation of Python's Timsort
   * Based on code by Christopher Swenson under the MIT license
   *
   * Copyright (c) 2010 Christopher Swenson
   * Copyright (c) 2011 Vicent Marti
   */
  
  #ifndef MAX
  #	define MAX(x,y) (((x) > (y) ? (x) : (y)))
  #endif
  
  #ifndef MIN
  #	define MIN(x,y) (((x) < (y) ? (x) : (y)))
  #endif
  
  static int binsearch(
  	void **dst, const void *x, size_t size, git__sort_r_cmp cmp, void *payload)
  {
  	int l, c, r;
  	void *lx, *cx;
  
  	l = 0;
  	r = (int)size - 1;
  	c = r >> 1;
  	lx = dst[l];
  
  	/* check for beginning conditions */
  	if (cmp(x, lx, payload) < 0)
  		return 0;
  
  	else if (cmp(x, lx, payload) == 0) {
  		int i = 1;
  		while (cmp(x, dst[i], payload) == 0)
  			i++;
  		return i;
  	}
  
  	/* guaranteed not to be >= rx */
  	cx = dst[c];
  	while (1) {
  		const int val = cmp(x, cx, payload);
  		if (val < 0) {
  			if (c - l <= 1) return c;
  			r = c;
  		} else if (val > 0) {
  			if (r - c <= 1) return c + 1;
  			l = c;
  			lx = cx;
  		} else {
  			do {
  				cx = dst[++c];
  			} while (cmp(x, cx, payload) == 0);
  			return c;
  		}
  		c = l + ((r - l) >> 1);
  		cx = dst[c];
  	}
  }
  
  /* Binary insertion sort, but knowing that the first "start" entries are sorted. Used in timsort. */
  static void bisort(
  	void **dst, size_t start, size_t size, git__sort_r_cmp cmp, void *payload)
  {
  	size_t i;
  	void *x;
  	int location;
  
  	for (i = start; i < size; i++) {
  		int j;
  		/* If this entry is already correct, just move along */
  		if (cmp(dst[i - 1], dst[i], payload) <= 0)
  			continue;
  
  		/* Else we need to find the right place, shift everything over, and squeeze in */
  		x = dst[i];
  		location = binsearch(dst, x, i, cmp, payload);
  		for (j = (int)i - 1; j >= location; j--) {
  			dst[j + 1] = dst[j];
  		}
  		dst[location] = x;
  	}
  }
  
  
  /* timsort implementation, based on timsort.txt */
  struct tsort_run {
  	ssize_t start;
  	ssize_t length;
  };
  
  struct tsort_store {
  	size_t alloc;
  	git__sort_r_cmp cmp;
  	void *payload;
  	void **storage;
  };
  
  static void reverse_elements(void **dst, ssize_t start, ssize_t end)
  {
  	while (start < end) {
  		void *tmp = dst[start];
  		dst[start] = dst[end];
  		dst[end] = tmp;
  
  		start++;
  		end--;
  	}
  }
  
  static ssize_t count_run(
  	void **dst, ssize_t start, ssize_t size, struct tsort_store *store)
  {
  	ssize_t curr = start + 2;
  
  	if (size - start == 1)
  		return 1;
  
  	if (start >= size - 2) {
  		if (store->cmp(dst[size - 2], dst[size - 1], store->payload) > 0) {
  			void *tmp = dst[size - 1];
  			dst[size - 1] = dst[size - 2];
  			dst[size - 2] = tmp;
  		}
  
  		return 2;
  	}
  
  	if (store->cmp(dst[start], dst[start + 1], store->payload) <= 0) {
  		while (curr < size - 1 &&
  				store->cmp(dst[curr - 1], dst[curr], store->payload) <= 0)
  			curr++;
  
  		return curr - start;
  	} else {
  		while (curr < size - 1 &&
  				store->cmp(dst[curr - 1], dst[curr], store->payload) > 0)
  			curr++;
  
  		/* reverse in-place */
  		reverse_elements(dst, start, curr - 1);
  		return curr - start;
  	}
  }
  
  static size_t compute_minrun(size_t n)
  {
  	int r = 0;
  	while (n >= 64) {
  		r |= n & 1;
  		n >>= 1;
  	}
  	return n + r;
  }
  
  static int check_invariant(struct tsort_run *stack, ssize_t stack_curr)
  {
  	if (stack_curr < 2)
  		return 1;
  
  	else if (stack_curr == 2) {
  		const ssize_t A = stack[stack_curr - 2].length;
  		const ssize_t B = stack[stack_curr - 1].length;
  		return (A > B);
  	} else {
  		const ssize_t A = stack[stack_curr - 3].length;
  		const ssize_t B = stack[stack_curr - 2].length;
  		const ssize_t C = stack[stack_curr - 1].length;
  		return !((A <= B + C) || (B <= C));
  	}
  }
  
  static int resize(struct tsort_store *store, size_t new_size)
  {
  	if (store->alloc < new_size) {
  		void **tempstore;
  
  		tempstore = git__reallocarray(store->storage, new_size, sizeof(void *));
  
  		/**
  		 * Do not propagate on OOM; this will abort the sort and
  		 * leave the array unsorted, but no error code will be
  		 * raised
  		 */
  		if (tempstore == NULL)
  			return -1;
  
  		store->storage = tempstore;
  		store->alloc = new_size;
  	}
  
  	return 0;
  }
  
  static void merge(void **dst, const struct tsort_run *stack, ssize_t stack_curr, struct tsort_store *store)
  {
  	const ssize_t A = stack[stack_curr - 2].length;
  	const ssize_t B = stack[stack_curr - 1].length;
  	const ssize_t curr = stack[stack_curr - 2].start;
  
  	void **storage;
  	ssize_t i, j, k;
  
  	if (resize(store, MIN(A, B)) < 0)
  		return;
  
  	storage = store->storage;
  
  	/* left merge */
  	if (A < B) {
  		memcpy(storage, &dst[curr], A * sizeof(void *));
  		i = 0;
  		j = curr + A;
  
  		for (k = curr; k < curr + A + B; k++) {
  			if ((i < A) && (j < curr + A + B)) {
  				if (store->cmp(storage[i], dst[j], store->payload) <= 0)
  					dst[k] = storage[i++];
  				else
  					dst[k] = dst[j++];
  			} else if (i < A) {
  				dst[k] = storage[i++];
  			} else
  				dst[k] = dst[j++];
  		}
  	} else {
  		memcpy(storage, &dst[curr + A], B * sizeof(void *));
  		i = B - 1;
  		j = curr + A - 1;
  
  		for (k = curr + A + B - 1; k >= curr; k--) {
  			if ((i >= 0) && (j >= curr)) {
  				if (store->cmp(dst[j], storage[i], store->payload) > 0)
  					dst[k] = dst[j--];
  				else
  					dst[k] = storage[i--];
  			} else if (i >= 0)
  				dst[k] = storage[i--];
  			else
  				dst[k] = dst[j--];
  		}
  	}
  }
  
  static ssize_t collapse(void **dst, struct tsort_run *stack, ssize_t stack_curr, struct tsort_store *store, ssize_t size)
  {
  	ssize_t A, B, C;
  
  	while (1) {
  		/* if the stack only has one thing on it, we are done with the collapse */
  		if (stack_curr <= 1)
  			break;
  
  		/* if this is the last merge, just do it */
  		if ((stack_curr == 2) && (stack[0].length + stack[1].length == size)) {
  			merge(dst, stack, stack_curr, store);
  			stack[0].length += stack[1].length;
  			stack_curr--;
  			break;
  		}
  
  		/* check if the invariant is off for a stack of 2 elements */
  		else if ((stack_curr == 2) && (stack[0].length <= stack[1].length)) {
  			merge(dst, stack, stack_curr, store);
  			stack[0].length += stack[1].length;
  			stack_curr--;
  			break;
  		}
  		else if (stack_curr == 2)
  			break;
  
  		A = stack[stack_curr - 3].length;
  		B = stack[stack_curr - 2].length;
  		C = stack[stack_curr - 1].length;
  
  		/* check first invariant */
  		if (A <= B + C) {
  			if (A < C) {
  				merge(dst, stack, stack_curr - 1, store);
  				stack[stack_curr - 3].length += stack[stack_curr - 2].length;
  				stack[stack_curr - 2] = stack[stack_curr - 1];
  				stack_curr--;
  			} else {
  				merge(dst, stack, stack_curr, store);
  				stack[stack_curr - 2].length += stack[stack_curr - 1].length;
  				stack_curr--;
  			}
  		} else if (B <= C) {
  			merge(dst, stack, stack_curr, store);
  			stack[stack_curr - 2].length += stack[stack_curr - 1].length;
  			stack_curr--;
  		} else
  			break;
  	}
  
  	return stack_curr;
  }
  
  #define PUSH_NEXT() do {\
  	len = count_run(dst, curr, size, store);\
  	run = minrun;\
  	if (run > (ssize_t)size - curr) run = size - curr;\
  	if (run > len) {\
  		bisort(&dst[curr], len, run, cmp, payload);\
  		len = run;\
  	}\
  	run_stack[stack_curr].start = curr;\
  	run_stack[stack_curr++].length = len;\
  	curr += len;\
  	if (curr == (ssize_t)size) {\
  		/* finish up */ \
  		while (stack_curr > 1) { \
  			merge(dst, run_stack, stack_curr, store); \
  			run_stack[stack_curr - 2].length += run_stack[stack_curr - 1].length; \
  			stack_curr--; \
  		} \
  		if (store->storage != NULL) {\
  			git__free(store->storage);\
  			store->storage = NULL;\
  		}\
  		return;\
  	}\
  }\
  while (0)
  
  void git__tsort_r(
  	void **dst, size_t size, git__sort_r_cmp cmp, void *payload)
  {
  	struct tsort_store _store, *store = &_store;
  	struct tsort_run run_stack[128];
  
  	ssize_t stack_curr = 0;
  	ssize_t len, run;
  	ssize_t curr = 0;
  	ssize_t minrun;
  
  	if (size < 64) {
  		bisort(dst, 1, size, cmp, payload);
  		return;
  	}
  
  	/* compute the minimum run length */
  	minrun = (ssize_t)compute_minrun(size);
  
  	/* temporary storage for merges */
  	store->alloc = 0;
  	store->storage = NULL;
  	store->cmp = cmp;
  	store->payload = payload;
  
  	PUSH_NEXT();
  	PUSH_NEXT();
  	PUSH_NEXT();
  
  	while (1) {
  		if (!check_invariant(run_stack, stack_curr)) {
  			stack_curr = collapse(dst, run_stack, stack_curr, store, size);
  			continue;
  		}
  
  		PUSH_NEXT();
  	}
  }
  
  static int tsort_r_cmp(const void *a, const void *b, void *payload)
  {
  	return ((git__tsort_cmp)payload)(a, b);
  }
  
  void git__tsort(void **dst, size_t size, git__tsort_cmp cmp)
  {
  	git__tsort_r(dst, size, tsort_r_cmp, cmp);
  }
  

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