Overhaul Make makefiles

* Header files and correspondent C sources that define
    functions recently added to public API moved from
    'tools' directory to root

  * By default, install prefix is '/usr/local/', and header
    install path is '${PREFIX}/include/kissfft'

  * Added detection of external libraries like FFTW or libPNG

Signed-off-by: Vasyl Gello <vasek.gello@gmail.com>

kfc.c

@@ -0,0 +1,109 @@
+/*
+ *  Copyright (c) 2003-2004, Mark Borgerding. All rights reserved.
+ *  This file is part of KISS FFT - https://github.com/mborgerding/kissfft
+ *
+ *  SPDX-License-Identifier: BSD-3-Clause
+ *  See COPYING file for more information.
+ */
+
+#include "kfc.h"
+
+typedef struct cached_fft *kfc_cfg;
+
+struct cached_fft
+{
+    int nfft;
+    int inverse;
+    kiss_fft_cfg cfg;
+    kfc_cfg next;
+};
+
+static kfc_cfg cache_root=NULL;
+static int ncached=0;
+
+static kiss_fft_cfg find_cached_fft(int nfft,int inverse)
+{
+    size_t len;
+    kfc_cfg  cur=cache_root;
+    kfc_cfg  prev=NULL;
+    while ( cur ) {
+        if ( cur->nfft == nfft && inverse == cur->inverse )
+            break;/*found the right node*/
+        prev = cur;
+        cur = prev->next;
+    }
+    if (cur== NULL) {
+        /* no cached node found, need to create a new one*/
+        kiss_fft_alloc(nfft,inverse,0,&len);
+#ifdef USE_SIMD
+        int padding = (16-sizeof(struct cached_fft)) & 15;
+        // make sure the cfg aligns on a 16 byte boundary
+        len += padding;
+#endif
+        cur = (kfc_cfg)KISS_FFT_MALLOC((sizeof(struct cached_fft) + len ));
+        if (cur == NULL)
+            return NULL;
+        cur->cfg = (kiss_fft_cfg)(cur+1);
+#ifdef USE_SIMD
+        cur->cfg = (kiss_fft_cfg) ((char*)(cur+1)+padding);
+#endif
+        kiss_fft_alloc(nfft,inverse,cur->cfg,&len);
+        cur->nfft=nfft;
+        cur->inverse=inverse;
+        cur->next = NULL;
+        if ( prev )
+            prev->next = cur;
+        else
+            cache_root = cur;
+        ++ncached;
+    }
+    return cur->cfg;
+}
+
+void kfc_cleanup(void)
+{
+    kfc_cfg  cur=cache_root;
+    kfc_cfg  next=NULL;
+    while (cur){
+        next = cur->next;
+        free(cur);
+        cur=next;
+    }
+    ncached=0;
+    cache_root = NULL;
+}
+void kfc_fft(int nfft, const kiss_fft_cpx * fin,kiss_fft_cpx * fout)
+{
+    kiss_fft( find_cached_fft(nfft,0),fin,fout );
+}
+
+void kfc_ifft(int nfft, const kiss_fft_cpx * fin,kiss_fft_cpx * fout)
+{
+    kiss_fft( find_cached_fft(nfft,1),fin,fout );
+}
+
+#ifdef KFC_TEST
+static void check(int nc)
+{
+    if (ncached != nc) {
+        fprintf(stderr,"ncached should be %d,but it is %d\n",nc,ncached);
+        exit(1);
+    }
+}
+
+int main(void)
+{
+    kiss_fft_cpx buf1[1024],buf2[1024];
+    memset(buf1,0,sizeof(buf1));
+    check(0);
+    kfc_fft(512,buf1,buf2);
+    check(1);
+    kfc_fft(512,buf1,buf2);
+    check(1);
+    kfc_ifft(512,buf1,buf2);
+    check(2);
+    kfc_cleanup();
+    check(0);
+    return 0;
+}
+#endif