From 07cc0809228236c7fdcab6b61c4d515f9b93dc84 Mon Sep 17 00:00:00 2001 From: Massimo Valentini Date: Sat, 14 Jul 2012 17:07:38 +0200 Subject: [PATCH] extensions/gggl{,-lies}.c: fix conversions u16 <-> u8 u16 maximum value is 0x10000 - 1 == (0x100 - 1) (0x100 + 1) u8 maximum value is 0x100 - 1 thus the direct conversion requires multiplication/division per 0x100+1 division per 0x100+1 is implemented using 1 term of (1 + x)^-1 MacLaurin expansion (1+x)^-1 == 1 + (-1) x a * (1 + 1/256)^-1 * (256^-1) == (a - a / 256) / 256 with integer division rounded toward the nearest. --- extensions/gggl-lies.c | 5 +++-- extensions/gggl.c | 5 +++-- 2 files changed, 6 insertions(+), 4 deletions(-) diff --git a/extensions/gggl-lies.c b/extensions/gggl-lies.c index 450fd75..7f99b00 100644 --- a/extensions/gggl-lies.c +++ b/extensions/gggl-lies.c @@ -342,7 +342,8 @@ conv_16_8 (unsigned char *src, unsigned char *dst, long samples) while (n--) { - (*(unsigned char *) dst) = (*(unsigned short *) src) >> 8; +#define div_257(a) ((((a)+128)-(((a)+128)>>8))>>8) + (*(unsigned char *) dst) = div_257 (*(unsigned short *) src); dst += 1; src += 2; } @@ -356,7 +357,7 @@ conv_8_16 (unsigned char *src, unsigned char *dst, long samples) while (n--) { - (*(unsigned short *) dst) = (*(unsigned char *) src) << 8; + (*(unsigned short *) dst) = ((*(unsigned char *) src) << 8) | *src; dst += 2; src += 1; } diff --git a/extensions/gggl.c b/extensions/gggl.c index c530988..307c574 100644 --- a/extensions/gggl.c +++ b/extensions/gggl.c @@ -380,7 +380,8 @@ conv_16_8 (unsigned char *src, unsigned char *dst, long samples) while (n--) { - (*(unsigned char *) dst) = (*(unsigned short *) src) >> 8; +#define div_257(a) ((((a)+128)-(((a)+128)>>8))>>8) + (*(unsigned char *) dst) = div_257 (*(unsigned short *) src); dst += 1; src += 2; } @@ -394,7 +395,7 @@ conv_8_16 (unsigned char *src, unsigned char *dst, long samples) while (n--) { - (*(unsigned short *) dst) = (*(unsigned char *) src) << 8; + (*(unsigned short *) dst) = ((*(unsigned char *) src) << 8) | *src; dst += 2; src += 1; } -- 2.30.2