diff --git a/libavcodec/dct-test.c b/libavcodec/dct-test.c
index 1da23a1d8e..98848dcbf8 100644
--- a/libavcodec/dct-test.c
+++ b/libavcodec/dct-test.c
@@ -6,12 +6,21 @@
 #include <string.h>
 #include <sys/time.h>
 #include <unistd.h>
+#include <getopt.h>
 
 #include "dsputil.h"
 
+#include "i386/mmx.h"
+
+/* reference fdct/idct */
 extern void fdct(DCTELEM *block);
+extern void idct(DCTELEM *block);
 extern void init_fdct();
 
+extern void j_rev_dct(DCTELEM *data);
+extern void ff_mmx_idct(DCTELEM *data);
+extern void ff_mmxext_idct(DCTELEM *data);
+
 #define AANSCALE_BITS 12
 static const unsigned short aanscales[64] = {
     /* precomputed values scaled up by 14 bits */
@@ -35,11 +44,26 @@ INT64 gettime(void)
 #define NB_ITS 20000
 #define NB_ITS_SPEED 50000
 
-void dct_error(const char *name,
-               void (*fdct_func)(DCTELEM *block))
+static short idct_mmx_perm[64];
+
+void idct_mmx_init(void)
+{
+    int i;
+
+    /* the mmx/mmxext idct uses a reordered input, so we patch scan tables */
+    for (i = 0; i < 64; i++) {
+	idct_mmx_perm[i] = (i & 0x38) | ((i & 6) >> 1) | ((i & 1) << 2);
+    }
+}
+
+static DCTELEM block[64] __attribute__ ((aligned (8)));
+static DCTELEM block1[64] __attribute__ ((aligned (8)));
+
+void dct_error(const char *name, int is_idct,
+               void (*fdct_func)(DCTELEM *block),
+               void (*fdct_ref)(DCTELEM *block))
 {
     int it, i, scale;
-    DCTELEM block[64], block1[64];
     int err_inf, v;
     INT64 err2, ti, ti1, it1;
 
@@ -50,9 +74,22 @@ void dct_error(const char *name,
     for(it=0;it<NB_ITS;it++) {
         for(i=0;i<64;i++) 
             block1[i] = random() % 256;
-        memcpy(block, block1, sizeof(DCTELEM) * 64);
-        
+
+        /* for idct test, generate inverse idct data */
+        if (is_idct)
+            fdct(block1);
+
+        if (fdct_func == ff_mmx_idct ||
+            fdct_func == j_rev_dct) {
+            for(i=0;i<64;i++) 
+                block[idct_mmx_perm[i]] = block1[i];
+        } else {
+            memcpy(block, block1, sizeof(DCTELEM) * 64);
+        }
+
         fdct_func(block);
+        emms(); /* for ff_mmx_idct */
+
         if (fdct_func == jpeg_fdct_ifast) {
             for(i=0; i<64; i++) {
                 scale = (1 << (AANSCALE_BITS + 11)) / aanscales[i];
@@ -60,7 +97,7 @@ void dct_error(const char *name,
             }
         }
 
-        fdct(block1);
+        fdct_ref(block1);
 
         for(i=0;i<64;i++) {
             v = abs(block[i] - block1[i]);
@@ -69,13 +106,23 @@ void dct_error(const char *name,
             err2 += v * v;
         }
     }
-    printf("DCT %s: err_inf=%d err2=%0.2f\n", 
+    printf("%s %s: err_inf=%d err2=%0.2f\n", 
+           is_idct ? "IDCT" : "DCT",
            name, err_inf, (double)err2 / NB_ITS / 64.0);
 
     /* speed test */
     for(i=0;i<64;i++) 
         block1[i] = 255 - 63 + i;
 
+    /* for idct test, generate inverse idct data */
+    if (is_idct)
+        fdct(block1);
+    if (fdct_func == ff_mmx_idct ||
+        fdct_func == j_rev_dct) {
+        for(i=0;i<64;i++) 
+            block[idct_mmx_perm[i]] = block1[i];
+    }
+
     ti = gettime();
     it1 = 0;
     do {
@@ -86,20 +133,53 @@ void dct_error(const char *name,
         it1 += NB_ITS_SPEED;
         ti1 = gettime() - ti;
     } while (ti1 < 1000000);
+    emms();
 
-    printf("DCT %s: %0.1f kdct/s\n", 
+    printf("%s %s: %0.1f kdct/s\n", 
+           is_idct ? "IDCT" : "DCT",
            name, (double)it1 * 1000.0 / (double)ti1);
 }
 
+void help(void)
+{
+    printf("dct-test [-i]\n"
+           "test DCT implementations\n");
+    exit(1);
+}
+
 int main(int argc, char **argv)
 {
-    init_fdct();
-    
-    printf("ffmpeg DCT test\n");
+    int test_idct = 0;
+    int c;
 
-    dct_error("REF", fdct); /* only to verify code ! */
-    dct_error("AAN", jpeg_fdct_ifast);
-    dct_error("MMX", fdct_mmx);
+    init_fdct();
+    idct_mmx_init();
+
+    for(;;) {
+        c = getopt(argc, argv, "ih");
+        if (c == -1)
+            break;
+        switch(c) {
+        case 'i':
+            test_idct = 1;
+            break;
+        case 'h':
+            help();
+            break;
+        }
+    }
+               
+    printf("ffmpeg DCT/IDCT test\n");
+
+    if (!test_idct) {
+        dct_error("REF", 0, fdct, fdct); /* only to verify code ! */
+        dct_error("AAN", 0, jpeg_fdct_ifast, fdct);
+        dct_error("MMX", 0, fdct_mmx, fdct);
+    } else {
+        dct_error("REF", 1, idct, idct);
+        dct_error("INT", 1, j_rev_dct, idct);
+        dct_error("MMX", 1, ff_mmx_idct, idct);
+        //    dct_error("MMX", 1, ff_mmxext_idct, idct);
+    }
     return 0;
 }
-