static MagickBooleanType sixel_encode_impl(unsigned char *pixels, size_t width,size_t height,
                  unsigned char *palette, size_t ncolors, int keycolor,
                  sixel_output_t *context)
{
#define RelinquishNodesAndMap \
    while ((np = context->node_free) != NULL) { \
        context->node_free = np->next; \
        np=(sixel_node_t *) RelinquishMagickMemory(np); \
    } \
    map = (unsigned char *) RelinquishMagickMemory(map)

    int x, y, i, n, c;
    int left, right;
    int len, pix;
    unsigned char *map;
    sixel_node_t *np, *tp, top;
    int nwrite;

    context->pos = 0;

    if (ncolors < 1) {
        return (MagickFalse);
    }
    len = ncolors * width;
    context->active_palette = (-1);

    if ((map = (unsigned char *)AcquireQuantumMemory(len, sizeof(unsigned char))) == NULL) {
        return (MagickFalse);
    }
    (void) ResetMagickMemory(map, 0, len);

    if (context->has_8bit_control) {
        nwrite = sprintf((char *)context->buffer, "\x90" "0;0;0" "q");
    } else {
        nwrite = sprintf((char *)context->buffer, "\x1bP" "0;0;0" "q");
    }
    if (nwrite <= 0) {
        return (MagickFalse);
    }
    sixel_advance(context, nwrite);
    nwrite = sprintf((char *)context->buffer + context->pos, "\"1;1;%d;%d", (int) width, (int) height);
    if (nwrite <= 0) {
        RelinquishNodesAndMap;
        return (MagickFalse);
    }
    sixel_advance(context, nwrite);

    if (ncolors != 2 || keycolor == -1) {
        for (n = 0; n < (ssize_t) ncolors; n++) {
            /* DECGCI Graphics Color Introducer  # Pc ; Pu; Px; Py; Pz */
            nwrite = sprintf((char *)context->buffer + context->pos, "#%d;2;%d;%d;%d",
                             n,
                             (palette[n * 3 + 0] * 100 + 127) / 255,
                             (palette[n * 3 + 1] * 100 + 127) / 255,
                             (palette[n * 3 + 2] * 100 + 127) / 255);
            if (nwrite <= 0) {
                RelinquishNodesAndMap;
                return (MagickFalse);
            }
            sixel_advance(context, nwrite);
            if (nwrite <= 0) {
                RelinquishNodesAndMap;
                return (MagickFalse);
            }
        }
    }

    for (y = i = 0; y < (ssize_t) height; y++) {
        for (x = 0; x < (ssize_t) width; x++) {
            pix = pixels[y * width + x];
            if (pix >= 0 && pix < (ssize_t) ncolors && pix != keycolor) {
                map[pix * width + x] |= (1 << i);
            }
        }

        if (++i < 6 && (y + 1) < (ssize_t) height) {
            continue;
        }

        for (c = 0; c < (ssize_t) ncolors; c++) {
            for (left = 0; left < (ssize_t) width; left++) {
                if (*(map + c * width + left) == 0) {
                    continue;
                }

                for (right = left + 1; right < (ssize_t) width; right++) {
                    if (*(map + c * width + right) != 0) {
                        continue;
                    }

                    for (n = 1; (right + n) < (ssize_t) width; n++) {
                        if (*(map + c * width + right + n) != 0) {
                            break;
                        }
                    }

                    if (n >= 10 || right + n >= (ssize_t) width) {
                        break;
                    }
                    right = right + n - 1;
                }

                if ((np = context->node_free) != NULL) {
                    context->node_free = np->next;
                } else if ((np = (sixel_node_t *)AcquireMagickMemory(sizeof(sixel_node_t))) == NULL) {
                    RelinquishNodesAndMap;
                    return (MagickFalse);
                }

                np->color = c;
                np->left = left;
                np->right = right;
                np->map = map + c * width;

                top.next = context->node_top;
                tp = &top;

                while (tp->next != NULL) {
                    if (np->left < tp->next->left) {
                        break;
                    }
                    if (np->left == tp->next->left && np->right > tp->next->right) {
                        break;
                    }
                    tp = tp->next;
                }

                np->next = tp->next;
                tp->next = np;
                context->node_top = top.next;

                left = right - 1;
            }

        }

        for (x = 0; (np = context->node_top) != NULL;) {
            if (x > np->left) {
                /* DECGCR Graphics Carriage Return */
                context->buffer[context->pos] = '$';
                sixel_advance(context, 1);
                x = 0;
            }

            x = sixel_put_node(context, x, np, ncolors, keycolor);
            sixel_node_del(context, np);
            np = context->node_top;

            while (np != NULL) {
                if (np->left < x) {
                    np = np->next;
                    continue;
                }

                x = sixel_put_node(context, x, np, ncolors, keycolor);
                sixel_node_del(context, np);
                np = context->node_top;
            }
        }

        /* DECGNL Graphics Next Line */
        context->buffer[context->pos] = '-';
        sixel_advance(context, 1);
        if (nwrite <= 0) {
            RelinquishNodesAndMap;
            return (MagickFalse);
        }

        i = 0;
        (void) ResetMagickMemory(map, 0, len);
    }

    if (context->has_8bit_control) {
        context->buffer[context->pos] = 0x9c;
        sixel_advance(context, 1);
    } else {
        context->buffer[context->pos] = 0x1b;
        context->buffer[context->pos + 1] = '\\';
        sixel_advance(context, 2);
    }
    if (nwrite <= 0) {
        RelinquishNodesAndMap;
        return (MagickFalse);
    }

    /* flush buffer */
    if (context->pos > 0) {
        (void) WriteBlob(context->image,context->pos,context->buffer);
    }

    RelinquishNodesAndMap;

    return(MagickTrue);
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.