};
struct mdct_context {
- /** Size of MDCT (i.e. number of input data * 2). */
+ /** Size of MDCT (number of input data * 2). */
int n;
/** n = 2^n bits. */
int nbits;
- /** pre/post rotation tables */
+ /** Cosine table for pre/post rotation. */
fftsample_t *tcos;
+ /** Sine table for pre/post rotation. */
fftsample_t *tsin;
+ /** The context for the underlying fast Fourier transform. */
struct fft_context fft;
};
return split_radix_permutation(i, m) * 4 - 1;
}
-#define SQRTHALF (float)0.70710678118654752440 /* 1/sqrt(2) */
+/** 1 / sqrt(2). */
+#define SQRTHALF (float)0.70710678118654752440
#define BF(x,y,a,b) {\
x = a - b;\
}
/**
- * Compute the inverse MDCT of size N = 2^nbits.
+ * Compute the inverse MDCT.
*
+ * \param ctx The initialized context structure.
* \param output N samples.
* \param input N/2 samples.
+ *
+ * \sa \ref imdct_init().
*/
-void imdct(struct mdct_context *s, float *output, const float *input)
+void imdct(struct mdct_context *ctx, float *output, const float *input)
{
int k;
- int n = 1 << s->nbits;
+ int n = 1 << ctx->nbits;
int n2 = n >> 1;
int n4 = n >> 2;
- imdct_half(s, output + n4, input);
+ imdct_half(ctx, output + n4, input);
for (k = 0; k < n4; k++) {
output[k] = -output[n2 - k - 1];
return 0;
}
-static void fft_end(struct fft_context *ctx)
-{
- freep(&ctx->revtab);
-}
-
/**
* Initialize the inverse modified cosine transform.
+ *
+ * \param nbits The number of bits to use (4 <= \a nbits <= 18).
+ *
+ * \param result Opaque structure that must be passed to \ref imdct().
+ *
+ * \return Standard.
*/
int imdct_init(int nbits, struct mdct_context **result)
{
return ret;
}
+/**
+ * Deallocate imdct resources.
+ *
+ * \param ctx The pointer obtained by imdct_init().
+ */
void imdct_end(struct mdct_context *ctx)
{
- freep(&ctx->tcos);
- freep(&ctx->tsin);
- fft_end(&ctx->fft);
+ free(ctx->tcos);
+ free(ctx->tsin);
+ free(ctx->fft.revtab);
free(ctx);
}