漫话Redis源码之十三

sds是一个基础的数据的结构，这两个函数没有看得很透彻，先记录学习一下，后面调到了，再具体看看：

/* Render part of a sequence, so that render_sequence() call call this function
 * with different parts in order to create the full output without overflowing
 * the current terminal columns. */
sds sparklineRenderRange(sds output, struct sequence *seq, int rows, int offset, int len, int flags) {
    int j;
    double relmax = seq->max - seq->min;
    int steps = charset_len*rows;
    int row = 0;
    char *chars = zmalloc(len);
    int loop = 1;
    int opt_fill = flags & SPARKLINE_FILL;
    int opt_log = flags & SPARKLINE_LOG_SCALE;
 
    if (opt_log) {
        relmax = log(relmax+1);
    } else if (relmax == 0) {
        relmax = 1;
    }
 
    while(loop) {
        loop = 0;
        memset(chars,' ',len);
        for (j = 0; j < len; j++) {
            struct sample *s = &seq->samples[j+offset];
            double relval = s->value - seq->min;
            int step;
 
            if (opt_log) relval = log(relval+1);
            step = (int) (relval*steps)/relmax;
            if (step < 0) step = 0;
            if (step >= steps) step = steps-1;
 
            if (row < rows) {
                /* Print the character needed to create the sparkline */
                int charidx = step-((rows-row-1)*charset_len);
                loop = 1;
                if (charidx >= 0 && charidx < charset_len) {
                    chars[j] = opt_fill ? charset_fill[charidx] :
                                          charset[charidx];
                } else if(opt_fill && charidx >= charset_len) {
                    chars[j] = '|';
                }
            } else {
                /* Labels spacing */
                if (seq->labels && row-rows < label_margin_top) {
                    loop = 1;
                    break;
                }
                /* Print the label if needed. */
                if (s->label) {
                    int label_len = strlen(s->label);
                    int label_char = row - rows - label_margin_top;
 
                    if (label_len > label_char) {
                        loop = 1;
                        chars[j] = s->label[label_char];
                    }
                }
            }
        }
        if (loop) {
            row++;
            output = sdscatlen(output,chars,len);
            output = sdscatlen(output,"\n",1);
        }
    }
    zfree(chars);
    return output;
}
 
/* Turn a sequence into its ASCII representation */
sds sparklineRender(sds output, struct sequence *seq, int columns, int rows, int flags) {
    int j;
 
    for (j = 0; j < seq->length; j += columns) {
        int sublen = (seq->length-j) < columns ? (seq->length-j) : columns;
 
        if (j != 0) output = sdscatlen(output,"\n",1);
        output = sparklineRenderRange(output, seq, rows, j, sublen, flags);
    }
    return output;
}