zircon/kernel/include/kernel/cpu.h

// Copyright 2016 The Fuchsia Authors
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT

#ifndef ZIRCON_KERNEL_INCLUDE_KERNEL_CPU_H_
#define ZIRCON_KERNEL_INCLUDE_KERNEL_CPU_H_

#include <assert.h>
#include <stdint.h>

// types and routines for dealing with lists of cpus and cpu masks

typedef uint32_t cpu_mask_t;
typedef uint32_t cpu_num_t;

static_assert(SMP_MAX_CPUS <= sizeof(cpu_mask_t) * CHAR_BIT, "");

#define INVALID_CPU ((cpu_num_t)-1)
#define CPU_MASK_ALL ((cpu_mask_t)-1)

static inline bool is_valid_cpu_num(cpu_num_t num) { return (num < SMP_MAX_CPUS); }

static inline cpu_mask_t cpu_num_to_mask(cpu_num_t num) {
  if (!is_valid_cpu_num(num)) {
    return 0;
  }

  return ((cpu_mask_t)1u << num);
}

static inline cpu_mask_t mask_all_but_one(cpu_num_t num) {
  return CPU_MASK_ALL ^ cpu_num_to_mask(num);
}

static inline cpu_num_t highest_cpu_set(cpu_mask_t mask) {
  if (mask == 0) {
    return 0;
  }

  return (cpu_num_t)(sizeof(cpu_mask_t) * CHAR_BIT - 1) - __builtin_clz(mask);
}

static inline cpu_num_t lowest_cpu_set(cpu_mask_t mask) {
  if (mask == 0) {
    return 0;
  }

  return (cpu_num_t)(__builtin_ctz(mask));
}

// Removes one CPU from the mask and returns its ID.
//
// Returns INVALID_CPU if the mask is empty.
static inline cpu_num_t remove_cpu_from_mask(cpu_mask_t& mask) {
  if (mask == 0) {
    return INVALID_CPU;
  }
  cpu_num_t index_of_lowest_set_bit = __builtin_ffsl(mask) - 1;
  mask &= ~cpu_num_to_mask(index_of_lowest_set_bit);
  return index_of_lowest_set_bit;
}

#endif  // ZIRCON_KERNEL_INCLUDE_KERNEL_CPU_H_