From 8cf872a186b96085b1bb3a547afd598354ebeb87 Mon Sep 17 00:00:00 2001
From: Zheng Lv <lvzheng@google.com>
Date: Tue, 13 Sep 2022 14:40:52 +0800
Subject: [PATCH] Make CELT FFT twiddle complex type aligned
This makes kiss_twiddle_cpx 4-byte aligned (instead of 2-byte) for
fixed-point builds. Tested with an armv6j+nofp development board, CELT
encoding becomes 1.4x as fast, and decoding over 2x.
Performance gain is mostly attributed to the proper alignment of the
static const array mdct_twiddles960.
Co-authored-by: David Gao <davidgao@google.com>
Signed-off-by: Felicia Lim <flim@google.com>
---
celt/kiss_fft.h | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/celt/kiss_fft.h b/celt/kiss_fft.h
index bffa2bfad..267f72f99 100644
--- a/celt/kiss_fft.h
+++ b/celt/kiss_fft.h
@@ -52,6 +52,10 @@ extern "C" {
# define kiss_fft_scalar opus_int32
# define kiss_twiddle_scalar opus_int16
+/* Some 32-bit CPUs would load/store a kiss_twiddle_cpx with a single memory
+ * access, and could benefit from additional alignment.
+ */
+# define KISS_TWIDDLE_CPX_ALIGNMENT (sizeof(opus_int32))
#else
# ifndef kiss_fft_scalar
@@ -62,6 +66,12 @@ extern "C" {
# endif
#endif
+#if defined(__GNUC__) && defined(KISS_TWIDDLE_CPX_ALIGNMENT)
+#define KISS_TWIDDLE_CPX_ALIGNED __attribute__((aligned(KISS_TWIDDLE_CPX_ALIGNMENT)))
+#else
+#define KISS_TWIDDLE_CPX_ALIGNED
+#endif
+
typedef struct {
kiss_fft_scalar r;
kiss_fft_scalar i;
@@ -70,7 +80,7 @@ typedef struct {
typedef struct {
kiss_twiddle_scalar r;
kiss_twiddle_scalar i;
-}kiss_twiddle_cpx;
+} KISS_TWIDDLE_CPX_ALIGNED kiss_twiddle_cpx;
#define MAXFACTORS 8
/* e.g. an fft of length 128 has 4 factors
--
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