From c8b6fdaf2c0f07201c5b2079c51465544f1eea2f Mon Sep 17 00:00:00 2001 From: David Reid Date: Wed, 29 Jan 2020 18:50:50 +1000 Subject: [PATCH] Use fixed point arithmetic with s16 biquads. --- research/ma_lpf.h | 59 ++++++++++++++++++++++++++++++----------------- 1 file changed, 38 insertions(+), 21 deletions(-) diff --git a/research/ma_lpf.h b/research/ma_lpf.h index 119bc300..5574f3d4 100644 --- a/research/ma_lpf.h +++ b/research/ma_lpf.h @@ -145,6 +145,15 @@ ma_uint32 ma_lpf_get_latency(ma_lpf* pLPF); #if defined(MINIAUDIO_IMPLEMENTATION) +#ifndef MA_BIQUAD_FIXED_POINT_SHIFT +#define MA_BIQUAD_FIXED_POINT_SHIFT 14 +#endif + +static ma_int32 ma_biquad_float_to_fp(double x) +{ + return (ma_int32)(x * (1 << MA_BIQUAD_FIXED_POINT_SHIFT)); +} + ma_biquad_config ma_biquad_config_init(ma_format format, ma_uint32 channels, double a0, double a1, double a2, double b0, double b1, double b2) { ma_biquad_config config; @@ -196,11 +205,19 @@ ma_result ma_biquad_reinit(const ma_biquad_config* pConfig, ma_biquad* pBQ) pBQ->channels = pConfig->channels; /* Normalize. */ - pBQ->a1.f32 = (float)(pConfig->a1 / pConfig->a0); - pBQ->a2.f32 = (float)(pConfig->a2 / pConfig->a0); - pBQ->b0.f32 = (float)(pConfig->b0 / pConfig->a0); - pBQ->b1.f32 = (float)(pConfig->b1 / pConfig->a0); - pBQ->b2.f32 = (float)(pConfig->b2 / pConfig->a0); + if (pConfig->format == ma_format_f32) { + pBQ->a1.f32 = (float)(pConfig->a1 / pConfig->a0); + pBQ->a2.f32 = (float)(pConfig->a2 / pConfig->a0); + pBQ->b0.f32 = (float)(pConfig->b0 / pConfig->a0); + pBQ->b1.f32 = (float)(pConfig->b1 / pConfig->a0); + pBQ->b2.f32 = (float)(pConfig->b2 / pConfig->a0); + } else { + pBQ->a1.s32 = ma_biquad_float_to_fp(pConfig->a1 / pConfig->a0); + pBQ->a2.s32 = ma_biquad_float_to_fp(pConfig->a2 / pConfig->a0); + pBQ->b0.s32 = ma_biquad_float_to_fp(pConfig->b0 / pConfig->a0); + pBQ->b1.s32 = ma_biquad_float_to_fp(pConfig->b1 / pConfig->a0); + pBQ->b2.s32 = ma_biquad_float_to_fp(pConfig->b2 / pConfig->a0); + } return MA_SUCCESS; } @@ -233,25 +250,25 @@ static MA_INLINE void ma_biquad_process_pcm_frame_f32__direct_form_2_transposed( static MA_INLINE void ma_biquad_process_pcm_frame_s16__direct_form_2_transposed(ma_biquad* pBQ, ma_int16* pY, const ma_int16* pX) { ma_uint32 c; - const float a1 = pBQ->a1.f32; - const float a2 = pBQ->a2.f32; - const float b0 = pBQ->b0.f32; - const float b1 = pBQ->b1.f32; - const float b2 = pBQ->b2.f32; + const ma_int32 a1 = pBQ->a1.s32; + const ma_int32 a2 = pBQ->a2.s32; + const ma_int32 b0 = pBQ->b0.s32; + const ma_int32 b1 = pBQ->b1.s32; + const ma_int32 b2 = pBQ->b2.s32; for (c = 0; c < pBQ->channels; c += 1) { - float r1 = pBQ->r1[c].f32; - float r2 = pBQ->r2[c].f32; - float x = pX[c] / 32767.0f; /* s16 -> f32 */ - float y; + ma_int32 r1 = pBQ->r1[c].s32; + ma_int32 r2 = pBQ->r2[c].s32; + ma_int32 x = pX[c]; + ma_int32 y; - y = b0*x + r1; - r1 = b1*x - a1*y + r2; - r2 = b2*x - a2*y; + y = (b0*x + r1) >> MA_BIQUAD_FIXED_POINT_SHIFT; + r1 = (b1*x - a1*y + r2); + r2 = (b2*x - a2*y); - pY[c] = (ma_int16)ma_clamp((ma_int32)(y * 32767.0f), -32768, 32767); /* f32 -> s16 */ - pBQ->r1[c].f32 = r1; - pBQ->r2[c].f32 = r2; + pY[c] = (ma_int16)ma_clamp(y, -32768, 32767); + pBQ->r1[c].s32 = r1; + pBQ->r2[c].s32 = r2; } } @@ -270,7 +287,7 @@ ma_result ma_biquad_process_pcm_frames(ma_biquad* pBQ, void* pFramesOut, const v const float* pX = (const float*)pFramesIn; for (n = 0; n < frameCount; n += 1) { - ma_biquad_process_pcm_frame_f32__direct_form_2_transposed(pBQ, pY + n*pBQ->channels, pX + n*pBQ->channels); + ma_biquad_process_pcm_frame_f32__direct_form_2_transposed(pBQ, pY, pX); pY += pBQ->channels; pX += pBQ->channels; }