每日一抄 Go语言封装qsort快速排序函数

package qsort

/*
《GO语言高级编程》设计中案例，仅作为笔记进行收藏。
qsort快速排序函数是C语⾔的⾼阶函数，⽀持⽤于⾃定义排序⽐较函数，可以对任意类型的数组进⾏排序。
*/

//sort.go支持包

/*
#include <stdlib.h>
typedef int (*qsort_cmp_func_t)(const void* a, const void* b);
extern int  _cgo_qsort_compare(void* a, void* b);
*/
import "C"

import (
	"fmt"
	"reflect"
	"sync"
	"unsafe"
)

var go_qsort_compare_info struct {
	base     unsafe.Pointer
	elemnum  int
	elemsize int
	less     func(a, b int) bool
	sync.Mutex
}

//export _cgo_qsort_compare
func _cgo_qsort_compare(a, b unsafe.Pointer) C.int {
	var (
		base     = uintptr(go_qsort_compare_info.base)
		elemsize = uintptr(go_qsort_compare_info.elemsize)
		i        = int((uintptr(a) - base) / elemsize)
		j        = int((uintptr(b) - base) / elemsize)
	)
	switch {
	case go_qsort_compare_info.less(i, j):
		//v[i] < v[j]
		return -1
	case go_qsort_compare_info.less(i, j):
		//v[i] > v[j]
		return +1
	default:
		return 0
	}
}

func Slice(slice interface{}, less func(a, b int) bool) {
	sv := reflect.ValueOf(slice)
	if sv.Kind() != reflect.Slice {
		panic(fmt.Sprintf("qsort called with non-slice value of type %T", slice))
	}
	if sv.Len() == 0 {
		return
	}
	go_qsort_compare_info.Lock()
	defer go_qsort_compare_info.Unlock()
	defer func() {
		go_qsort_compare_info.base = nil
		go_qsort_compare_info.elemnum = 0
		go_qsort_compare_info.elemsize = 0
		go_qsort_compare_info.less = nil
	}()
	go_qsort_compare_info.base = unsafe.Pointer(sv.Index(0).Addr().Pointer())
	go_qsort_compare_info.elemnum = sv.Len()
	go_qsort_compare_info.elemsize = int(sv.Type().Elem().Size())
	go_qsort_compare_info.less = less
	C.qsort(
		go_qsort_compare_info.base,
		C.size_t(go_qsort_compare_info.elemnum),
		C.size_t(go_qsort_compare_info.elemsize),
		C.qsort_cmp_func_t(C._cgo_qsort_compare),
	)
}