On Wed, 16 Nov 2022 14:46:46 +0000
Valentin Schneider <vschneid@xxxxxxxxxx> wrote:
> +static void print_cpumask_to_seq(struct tep_handle *tep,
> + struct trace_seq *s, const char *format,
> + int len_arg, const void *data, int size)
> +{
> + int firstone = -1, firstzero = -1;
> + int nr_bits = size * 8;
> + bool first = true;
> + int str_size = 0;
> + char buf[12]; /* '-' + log10(2^32) + 1 digits + '\0' */
> + char *str;
> + int index;
> + int i;
> +
> + str = malloc(cpumask_worst_size(nr_bits) + 1);
> + if (!str) {
> + do_warning("%s: not enough memory!", __func__);
> + return;
> + }
> +
> + for (i = 0; i < size; i++) {
> + unsigned char byte;
> + int fmtsize;
> +
> + if (tep->file_bigendian)
> + index = size - (i + 1);
> + else
> + index = i;
> +
> + /* Byte by byte scan, not the best... */
> + byte = *(((unsigned char *)data) + index);
> +more:
> + /* First find a bit set to one...*/
> + if (firstone < 0 && byte) {
> + /*
> + * Set all lower bits, so a later ffz on this same byte
> + * is guaranteed to find a later bit.
> + */
> + firstone = ffs(byte) - 1;
> + byte |= (1 << firstone) - 1;
> + firstone += i * 8;
> + }
> +
> + if (firstone < 0)
> + continue;
> +
> + /* ...Then find a bit set to zero */
> + if ((~byte) & 0xFF) {
> + /*
> + * Clear all lower bits, so a later ffs on this same
> + * byte is guaranteed to find a later bit.
> + */
> + firstzero = ffs(~byte) - 1;
> + byte &= ~((1 << (firstzero)) - 1);
> + firstzero += i * 8;
> + } else if (i == size - 1) { /* ...Or reach the end of the mask */
> + firstzero = nr_bits;
> + byte = 0;
> + } else {
> + continue;
> + }
> +
> + /* We've found a bit set to one, and a later bit set to zero. */
> + if (!first) {
> + str[str_size] = ',';
> + str_size++;
> + }
> + first = false;
> +
> + /* It takes {log10(number) + 1} chars to format a number */
> + fmtsize = log10(firstone) + 1;
> + snprintf(buf, fmtsize + 1, "%d", firstone);
> + memcpy(str + str_size, buf, fmtsize);
> + str_size += fmtsize;
> +
> + if (firstzero > firstone + 1) {
> + fmtsize = log10(firstzero - 1) + 2;
> + snprintf(buf, fmtsize + 1, "-%d", firstzero - 1);
> + memcpy(str + str_size, buf, fmtsize);
> + str_size += fmtsize;
> + }
> +
> + firstzero = firstone = -1;
> + if (byte)
> + goto more;
> + }
> +
> + str[str_size] = 0;
> + str_size++;
> +
> + if (len_arg >= 0)
> + trace_seq_printf(s, format, len_arg, str);
> + else
> + trace_seq_printf(s, format, str);
> +
> + free(str);
> +}
> +
This is a rather complex algorithm (I'm too tired to try to grasp it). It
really needs a unit test to make sure it's working as expected.
-- Steve
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