de-recurse hist_item_sort_halfvar()

Signed-off-by: liubo <liubo1@xfusion.com>
(cherry picked from commit 80fc3ecada9cdad5d09c699ec166fbd1b04381aa)
(cherry picked from commit ee903edc24221a4807cdbd063dc4f4c2b20ce98b)

0001-de-recurse-hist_item_sort_halfvar.patch

@@ -0,0 +1,86 @@
+From fd3d56154cc55ab07628f8f2d37e77f60f17874c Mon Sep 17 00:00:00 2001
+From: Pascal Massimino <skal@google.com>
+Date: Mon, 8 Mar 2021 11:07:29 +0100
+Subject: [PATCH] de-recurse hist_item_sort_halfvar()
+
+This function can recurse quite deep when sorting values are
+quite flag. We remove the recursion call totally.
+The API is slightly changed to return the break_at index directly.
+---
+ mediancut.c | 37 +++++++++++++++++++------------------
+ 1 file changed, 19 insertions(+), 18 deletions(-)
+
+diff --git a/mediancut.c b/mediancut.c
+index 2c6d1d8..64a21f2 100644
+--- a/mediancut.c
++++ b/mediancut.c
+@@ -134,34 +134,36 @@ static void hist_item_sort_range(hist_item base[], unsigned int len, unsigned in
+ }
+ 
+ /** sorts array to make sum of weights lower than halfvar one side, returns edge between <halfvar and >halfvar parts of the set */
+-static hist_item *hist_item_sort_halfvar(hist_item base[], unsigned int len, double *const lowervar, const double halfvar)
++static unsigned int hist_item_sort_halfvar(hist_item base[], unsigned int len, double halfvar)
+ {
++    unsigned int base_idx = 0;  // track base-index
+     do {
+         const unsigned int l = qsort_partition(base, len), r = l+1;
+ 
+         // check if sum of left side is smaller than half,
+         // if it is, then it doesn't need to be sorted
+-        unsigned int t = 0; double tmpsum = *lowervar;
+-        while (t <= l && tmpsum < halfvar) tmpsum += base[t++].color_weight;
++        double tmpsum = 0.;
++        for(unsigned int t = 0; t <= l && tmpsum < halfvar; ++t) tmpsum += base[t].color_weight;
+ 
+-        if (tmpsum < halfvar) {
+-            *lowervar = tmpsum;
+-        } else {
++        // the split is on the left part
++        if (tmpsum >= halfvar) {
+             if (l > 0) {
+-                hist_item *res = hist_item_sort_halfvar(base, l, lowervar, halfvar);
+-                if (res) return res;
++                len = l;
++                continue;
+             } else {
+-                // End of left recursion. This will be executed in order from the first element.
+-                *lowervar += base[0].color_weight;
+-                if (*lowervar > halfvar) return &base[0];
++                // End of left recursion;
++                return base_idx;
+             }
+         }
+-
++        // process the right part
++        halfvar -= tmpsum;
+         if (len > r) {
+-            base += r; len -= r; // tail-recursive "call"
++            base += r;
++            base_idx += r;
++            len -= r; // tail-recursive "call"
+         } else {
+-            *lowervar += base[r].color_weight;
+-            return (*lowervar > halfvar) ? &base[r] : NULL;
++            // End of right recursion
++            return base_idx + len;
+         }
+     } while(1);
+ }
+@@ -370,12 +372,11 @@ LIQ_PRIVATE colormap *mediancut(histogram *hist, unsigned int newcolors, const d
+              */
+ 
+             const double halfvar = prepare_sort(&bv[bi], achv);
+-            double lowervar=0;
+ 
+             // hist_item_sort_halfvar sorts and sums lowervar at the same time
+             // returns item to break at …minus one, which does smell like an off-by-one error.
+-            hist_item *break_p = hist_item_sort_halfvar(&achv[indx], clrs, &lowervar, halfvar);
+-            unsigned int break_at = MIN(clrs-1, break_p - &achv[indx] + 1);
++            unsigned int break_at = hist_item_sort_halfvar(&achv[indx], clrs, halfvar);
++            break_at = MIN(clrs-1, break_at + 1);
+ 
+             /*
+              ** Split the box.
+-- 
+2.42.0.windows.2
+

libimagequant.spec

@@ -1,12 +1,14 @@
 Name:           libimagequant
 Version:        2.15.1
-Release:        2
+Release:        3
 Summary:        Palette quantization library
 License:        GPLv3+ and MIT
 URL:            https://github.com/ImageOptim/libimagequant
 Source0:        %{url}/archive/%{version}/%{name}-%{version}.tar.gz
 
 Patch0000:      libimagequant_solibperm.patch
+Patch0001:      0001-de-recurse-hist_item_sort_halfvar.patch
+
 
 BuildRequires:  gcc
 
@@ -47,6 +49,9 @@ rm -f %{buildroot}%{_libdir}/%{name}.a
 %{_libdir}/pkgconfig/imagequant.pc
 
 %changelog
+* Mon Oct 23 2023 liubo <liubo1@xfusion.com> - 2.15.1-3
+- de-recurse hist_item_sort_halfvar()
+
 * Wed Oct 26 2022 zhouwenpei <zhouwenpei1@h-partners.com> - 2.15.1-2
 - Rebuild for next release