1f6c81bc8d
Signed-off-by: liubo <liubo1@xfusion.com> (cherry picked from commit 80fc3ecada9cdad5d09c699ec166fbd1b04381aa) (cherry picked from commit ee903edc24221a4807cdbd063dc4f4c2b20ce98b)
87 lines
3.5 KiB
Diff
87 lines
3.5 KiB
Diff
From fd3d56154cc55ab07628f8f2d37e77f60f17874c Mon Sep 17 00:00:00 2001
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From: Pascal Massimino <skal@google.com>
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Date: Mon, 8 Mar 2021 11:07:29 +0100
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Subject: [PATCH] de-recurse hist_item_sort_halfvar()
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This function can recurse quite deep when sorting values are
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quite flag. We remove the recursion call totally.
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The API is slightly changed to return the break_at index directly.
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---
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mediancut.c | 37 +++++++++++++++++++------------------
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1 file changed, 19 insertions(+), 18 deletions(-)
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diff --git a/mediancut.c b/mediancut.c
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index 2c6d1d8..64a21f2 100644
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--- a/mediancut.c
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+++ b/mediancut.c
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@@ -134,34 +134,36 @@ static void hist_item_sort_range(hist_item base[], unsigned int len, unsigned in
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}
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/** sorts array to make sum of weights lower than halfvar one side, returns edge between <halfvar and >halfvar parts of the set */
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-static hist_item *hist_item_sort_halfvar(hist_item base[], unsigned int len, double *const lowervar, const double halfvar)
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+static unsigned int hist_item_sort_halfvar(hist_item base[], unsigned int len, double halfvar)
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{
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+ unsigned int base_idx = 0; // track base-index
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do {
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const unsigned int l = qsort_partition(base, len), r = l+1;
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// check if sum of left side is smaller than half,
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// if it is, then it doesn't need to be sorted
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- unsigned int t = 0; double tmpsum = *lowervar;
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- while (t <= l && tmpsum < halfvar) tmpsum += base[t++].color_weight;
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+ double tmpsum = 0.;
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+ for(unsigned int t = 0; t <= l && tmpsum < halfvar; ++t) tmpsum += base[t].color_weight;
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- if (tmpsum < halfvar) {
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- *lowervar = tmpsum;
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- } else {
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+ // the split is on the left part
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+ if (tmpsum >= halfvar) {
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if (l > 0) {
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- hist_item *res = hist_item_sort_halfvar(base, l, lowervar, halfvar);
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- if (res) return res;
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+ len = l;
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+ continue;
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} else {
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- // End of left recursion. This will be executed in order from the first element.
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- *lowervar += base[0].color_weight;
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- if (*lowervar > halfvar) return &base[0];
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+ // End of left recursion;
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+ return base_idx;
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}
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}
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-
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+ // process the right part
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+ halfvar -= tmpsum;
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if (len > r) {
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- base += r; len -= r; // tail-recursive "call"
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+ base += r;
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+ base_idx += r;
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+ len -= r; // tail-recursive "call"
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} else {
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- *lowervar += base[r].color_weight;
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- return (*lowervar > halfvar) ? &base[r] : NULL;
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+ // End of right recursion
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+ return base_idx + len;
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}
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} while(1);
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}
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@@ -370,12 +372,11 @@ LIQ_PRIVATE colormap *mediancut(histogram *hist, unsigned int newcolors, const d
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*/
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const double halfvar = prepare_sort(&bv[bi], achv);
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- double lowervar=0;
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// hist_item_sort_halfvar sorts and sums lowervar at the same time
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// returns item to break at …minus one, which does smell like an off-by-one error.
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- hist_item *break_p = hist_item_sort_halfvar(&achv[indx], clrs, &lowervar, halfvar);
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- unsigned int break_at = MIN(clrs-1, break_p - &achv[indx] + 1);
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+ unsigned int break_at = hist_item_sort_halfvar(&achv[indx], clrs, halfvar);
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+ break_at = MIN(clrs-1, break_at + 1);
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/*
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** Split the box.
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--
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2.42.0.windows.2
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