--- /dev/null
+diff -ur a/quantize.c b/quantize.c
+--- a/quantize.c 2019-02-11 07:43:57.000000000 -0700
++++ b/quantize.c 2019-02-27 17:20:06.369498072 -0700
+# SortRGBAxis is static and not locked, qsort recoded
+# GAErrorToken is also static and not locked, not fixed
+@@ -11,8 +11,9 @@
+
+ ******************************************************************************/
+
+-#include <stdlib.h>
+ #include <stdio.h>
++#include <stdlib.h>
++
+ #include "gif_lib.h"
+ #include "gif_lib_private.h"
+
+@@ -22,8 +23,6 @@
+ #define BITS_PER_PRIM_COLOR 5
+ #define MAX_PRIM_COLOR 0x1f
+
+-static int SortRGBAxis;
+-
+ typedef struct QuantizedColorType {
+ GifByteType RGB[3];
+ GifByteType NewColorIndex;
+@@ -31,6 +30,40 @@
+ struct QuantizedColorType *Pnext;
+ } QuantizedColorType;
+
++static int QCmpr(QuantizedColorType *a, QuantizedColorType *b, int i)
++{
++ int i0 = i, i1 = i+1, i2 = i+2;
++ if( i1 >= 3 ) i1 -= 3;
++ if( i2 >= 3 ) i2 -= 3;
++ /* sort on all axes of the color space! */
++ int hash_a = (a->RGB[i0] << 16) | (a->RGB[i1] << 8) | (a->RGB[i2] << 0);
++ int hash_b = (b->RGB[i0] << 16) | (b->RGB[i1] << 8) | (b->RGB[i2] << 0);
++ return hash_a - hash_b;
++}
++
++static int QSplit(QuantizedColorType **q, int l, int r, int i)
++{
++ int m;
++ QuantizedColorType *t;
++ for(;;) {
++ while( QCmpr(q[r],q[l], i) >= 0 ) if( ++l == r ) return r;
++ t = q[l]; q[l] = q[r]; q[r] = t; m = l; l = r; r = m;
++ while( QCmpr(q[l],q[r], i) >= 0 ) if( r == --l ) return r;
++ t = q[l]; q[l] = q[r]; q[r] = t; m = l; l = r; r = m;
++ }
++}
++
++static void QSort(QuantizedColorType **q, int ll, int rr, int i)
++{
++ for(;;) {
++ int l = ll+1; if( l == rr ) return;
++ int r = rr-1; if( l == r ) return;
++ int m = QSplit(q, l, r, i);
++ QSort(q, ll, m, i);
++ ll = m;
++ }
++}
++
+ typedef struct NewColorMapType {
+ GifByteType RGBMin[3], RGBWidth[3];
+ unsigned int NumEntries; /* # of QuantizedColorType in linked list below */
+@@ -41,7 +74,6 @@
+ static int SubdivColorMap(NewColorMapType * NewColorSubdiv,
+ unsigned int ColorMapSize,
+ unsigned int *NewColorMapSize);
+-static int SortCmpRtn(const void *Entry1, const void *Entry2);
+
+ /******************************************************************************
+ Quantize high resolution image into lower one. Input image consists of a
+@@ -198,6 +230,7 @@
+ unsigned int ColorMapSize,
+ unsigned int *NewColorMapSize) {
+
++ int SortRGBAxis = 0;
+ unsigned int i, j, Index = 0;
+ QuantizedColorType *QuantizedColor, **SortArray;
+
+@@ -234,19 +267,7 @@
+ j++, QuantizedColor = QuantizedColor->Pnext)
+ SortArray[j] = QuantizedColor;
+
+- /*
+- * Because qsort isn't stable, this can produce differing
+- * results for the order of tuples depending on platform
+- * details of how qsort() is implemented.
+- *
+- * We mitigate this problem by sorting on all three axes rather
+- * than only the one specied by SortRGBAxis; that way the instability
+- * can only become an issue if there are multiple color indices
+- * referring to identical RGB tuples. Older versions of this
+- * sorted on only the one axis.
+- */
+- qsort(SortArray, NewColorSubdiv[Index].NumEntries,
+- sizeof(QuantizedColorType *), SortCmpRtn);
++ QSort(SortArray, -1, NewColorSubdiv[Index].NumEntries, SortRGBAxis);
+
+ /* Relink the sorted list into one: */
+ for (j = 0; j < NewColorSubdiv[Index].NumEntries - 1; j++)
+@@ -310,21 +331,4 @@
+ Routine called by qsort to compare two entries.
+ *****************************************************************************/
+
+-static int
+-SortCmpRtn(const void *Entry1,
+- const void *Entry2) {
+- QuantizedColorType *entry1 = (*((QuantizedColorType **) Entry1));
+- QuantizedColorType *entry2 = (*((QuantizedColorType **) Entry2));
+-
+- /* sort on all axes of the color space! */
+- int hash1 = entry1->RGB[SortRGBAxis] * 256 * 256
+- + entry1->RGB[(SortRGBAxis+1) % 3] * 256
+- + entry1->RGB[(SortRGBAxis+2) % 3];
+- int hash2 = entry2->RGB[SortRGBAxis] * 256 * 256
+- + entry2->RGB[(SortRGBAxis+1) % 3] * 256
+- + entry2->RGB[(SortRGBAxis+2) % 3];
+-
+- return hash1 - hash2;
+-}
+-
+ /* end */