And support this includes:
<xmmintrin.h> SSE
<emmintrin.h> SSE2
<pmmintrin.h> SSE3
<tmmintrin.h> SSSE3
<smmintrin.h> SSE4.1
<nmmintrin.h> SSE4.2

What is the code size limit ?

// Simple windows gui program
#debug
#gui
#include "kernel32.h"
#include "user32.h"
#include "msvcrt.h"
char *msg = "Hi! I'm the example "
#ifdef _WIN64
"64"
#else
"32"
#endif
"-bit program!";
float floorf (float wx) {
      asm{  roundss xmm1,[wx],9
            movss  [wx],xmm1  }
        return wx;  }
//float lerpA(float a,float b,float t){ return a-(a*t)+(b*t); }
float Lerp(float a,float b,float t){ return (b*t); }
typedef struct vec4 {
    float x;
    float y;
    float z;
    float w;
} vec4;
void main(){
    float fir = 4;
    vec4  dif = {11,2,3,5};
    dif.x += fir;
    dif.y += fir;
    dif.z += fir;
    dif.w += fir;
    float height;
    float LvlSize = 110.0f;
    float CamX = 50.0f;
    float CamZ = 50.0f;
    float x = (55.0f + CamX) / 6.327272f;
    float z = (55.0f - CamZ) / 6.327272f;

    float col = floorf(x);
    float row = floorf(z);

    float A = 1.0f;
    float B = 2.0f;
    float C = 3.0f;
    float D = 4.0f;

    float dx = x - col;
    float dz = z - row;

    if(dz < 1.0f - dx)
     { float uy = B - A;
       float vy = C - A;
       height = A + Lerp(0.0f, uy, dx) + Lerp(0.0f, vy, dz);
      }
    else {
       float uy = C - D;
       float vy = B - D;
       height = D + Lerp(0.0f,uy,1.0f - dx) + Lerp(0.0f, vy, 1.0f - dz);
       }
    char rrt[100];
    char *tname = "result: %1.4f";
    sprintf(rrt,tname,height);
    MessageBox(HWND_DESKTOP,rrt,MB_OK,MB_OK);
    ExitProcess(0);
}
    

int foo = 12;

int main()
{
    return foo;
}
    

format PE  
include 'include\win32ax.inc'
entry main
section '.code' code readable executable

main:
        push    ebp
        mov     ebp,esp
.l0:
        mov     eax,dword[foo]
        mov     esp,ebp
        pop     ebp
        ret     0
section '.data' data readable writeable

__d_1   dq      1.000000

__f_1   dd      1.000000



section '.reloc' fixups data readable discardable
if $=$$
dd 0,8
end if
    

mov     eax,dword[foo]    

Symbol foo not used    

Symbol foo not used    

FlatC v.0.22 (fasm v.1.73)
fasm error#2 (minimal.asm:10)
Symbol foo not used
    

undefined symbol 'foo'    

section '.reloc' fixups data readable discardable
if $=$$
dd 0,8
end if 
    

Thank you for your interest in my compiler, rc.
I regret that I do not immediately answer, but I rarely visit the forum, and I do not receive alerts about new messages.
I fixed the error.
"The devil is hiding in the details"

#ifndef _ARRAY_H_
#define _ARRAY_H_

#include "stddef.h"  // including my stddef.h, this causes the strange error


typedef struct Array
{
        int *array;
        size_t used;
        size_t size;
} Array;

void arrayInit(Array *a, size_t initialSize)
{
        a->array = (int *)malloc(initialSize * sizeof(int));
        a->used = 0;
        a->size = initialSize;
}

void arrayInsert(Array *a, int element)
{
        if(a->used == a->size)
        {
                a->size *= 2;
                a->array = (int *)realloc(a->array, a->size * sizeof(int));
        }
}

void arrayFree(Array *a)
{
        free(a->array);
        a->array = NULL;
        a->used = a->size = 0;
}

#endif    

#ifndef _STDDEF_H
#define _STDDEF_H

#define NULL (void*)0
#define NUL 0x00

#endif    

#include "msvcrt.h"
#include "array.h"

int main()
{
        return 0;
}    

>flatc test.c
FlatC v.0.25 (fasm v.1.73)
(msvcrt.h,71): void srand(unsigned int);
error:maybe you accidently add the ;    

#ifndef _ARRAY_H_
#define _ARRAY_H_

#include "stddef.h" // <---


typedef struct Array
{

...

#endif    

#ifndef _ARRAY_H_
#define _ARRAY_H_

#define NULL (void*)0 // <---
#define NUL 0x00 // <---

typedef struct Array
{

...

#endif    

Thanks for the feedback.
The preprocessor is very primitive now and I plan to improve it in the future.
I suggest avoiding nesting include files in each other a while.