/*
  libco.x86 (2009-10-12)
  author: byuu
  license: public domain
*/

#define LIBCO_C
#include "libco.h"
#include <assert.h>
#include <stdlib.h>

#ifdef __cplusplus
extern "C" {
#endif

#if defined(_MSC_VER)
  #define fastcall __fastcall
#elif defined(__GNUC__)
  #define fastcall __attribute__((fastcall))
#else
  #error "libco: please define fastcall macro"
#endif

static thread_local long co_active_buffer[64];
static thread_local cothread_t co_active_handle = 0;
static void (fastcall *co_swap)(cothread_t, cothread_t) = 0;

//ABI: fastcall
static unsigned char co_swap_function[] = {
  0x89, 0x22,         /* mov [edx],esp      */
  0x8b, 0x21,         /* mov esp,[ecx]      */
  0x58,               /* pop eax            */
  0x89, 0x6a, 0x04,   /* mov [edx+0x04],ebp */
  0x89, 0x72, 0x08,   /* mov [edx+0x08],esi */
  0x89, 0x7a, 0x0c,   /* mov [edx+0x0c],edi */
  0x89, 0x5a, 0x10,   /* mov [edx+0x10],ebx */
  0x8b, 0x69, 0x04,   /* mov ebp,[ecx+0x04] */
  0x8b, 0x71, 0x08,   /* mov esi,[ecx+0x08] */
  0x8b, 0x79, 0x0c,   /* mov edi,[ecx+0x0c] */
  0x8b, 0x59, 0x10,   /* mov ebx,[ecx+0x10] */
  0xff, 0xe0,         /* jmp eax            */
};

#ifdef _WIN32
#include <windows.h>

void co_init(void)
{
   DWORD old_privileges;
   VirtualProtect(co_swap_function,
         sizeof co_swap_function, PAGE_EXECUTE_READWRITE, &old_privileges);
}
#else
#include <unistd.h>
#include <sys/mman.h>

void co_init(void)
{
   unsigned long addr = (unsigned long)co_swap_function;
   unsigned long base = addr - (addr % sysconf(_SC_PAGESIZE));
   unsigned long size = (addr - base) + sizeof co_swap_function;
   mprotect((void*)base, size, PROT_READ | PROT_WRITE | PROT_EXEC);
}
#endif

static void crash(void)
{
   assert(0); /* called only if cothread_t entrypoint returns */
}

cothread_t co_active(void)
{
   if(!co_active_handle)
      co_active_handle = &co_active_buffer;
   return co_active_handle;
}

cothread_t co_create(unsigned int size, void (*entrypoint)(void))
{
   cothread_t handle;
   if(!co_swap)
   {
      co_init();
      co_swap = (void (fastcall*)(cothread_t, cothread_t))co_swap_function;
   }

   if(!co_active_handle)
      co_active_handle = &co_active_buffer;

   size += 256; /* allocate additional space for storage */
   size &= ~15; /* align stack to 16-byte boundary */

   if((handle = (cothread_t)malloc(size)))
   {
      long *p = (long*)((char*)handle + size); /* seek to top of stack */
      *--p = (long)crash;                      /* crash if entrypoint returns */
      *--p = (long)entrypoint;                 /* start of function */
      *(long*)handle = (long)p;                /* stack pointer */
   }

   return handle;
}

void co_delete(cothread_t handle)
{
   free(handle);
}

void co_switch(cothread_t handle)
{
   register cothread_t co_previous_handle = co_active_handle;
   co_swap(co_active_handle = handle, co_previous_handle);
}

#ifdef __cplusplus
}
#endif
