shithub: rgbds

Info  •  Files  •  Log  •  Branches

Convert floating to fixed point by rounding, not truncation

Fixes #678

--- a/src/asm/lexer.c

+++ b/src/asm/lexer.c

@@ -13,6 +13,7 @@

 #include <errno.h>

 #include <fcntl.h>

 #include <inttypes.h>

+#include <math.h>

 #include <limits.h>

 #include <stdbool.h>

 #include <stdint.h>

@@ -1130,7 +1131,7 @@

 	/* Cast to unsigned avoids UB if shifting discards bits */

 	yylval.nConstValue = (uint32_t)yylval.nConstValue << 16;

 	/* Cast to unsigned avoids undefined overflow behavior */

-	uint16_t fractional = value * 65536 / divisor;

+	uint16_t fractional = (uint16_t)round(value * 65536.0 / divisor);

 	yylval.nConstValue |= fractional * (yylval.nConstValue >= 0 ? 1 : -1);

 }

--- a/src/asm/math.c

+++ b/src/asm/math.c

@@ -20,7 +20,7 @@

 #include "asm/warning.h"

 #define fx2double(i)	((double)((i) / 65536.0))

-#define double2fx(d)	((int32_t)((d) * 65536.0))

+#define double2fx(d)	((int32_t)round((d) * 65536.0))

 #ifndef M_PI

 #define M_PI 3.14159265358979323846

--- /dev/null

+++ b/test/asm/fixed-point-precision.asm

@@ -1,0 +1,11 @@

+f1 = 3.1

+f2 = 5.2

+pm = MUL(f1, f2)

+pr = 16.12

+	println "`3.1`:   {9.6f:f1} -> ${08x:f1}"

+	println "`5.2`:   {9.6f:f2} -> ${08x:f2}"

+	println "`MUL`:   {9.6f:pm} -> ${08x:pm}"

+	println "`16.12`: {9.6f:pr} -> ${08x:pr}"

+

+fl = 6.283185

+	println "`6.283185`: {.6f:fl} -> ${08x:fl}"

--- /dev/null

+++ b/test/asm/fixed-point-precision.out

@@ -1,0 +1,5 @@

+`3.1`:    3.100007 -> $0003199a

+`5.2`:    5.199997 -> $00053333

+`MUL`:   16.120026 -> $00101eba

+`16.12`: 16.119996 -> $00101eb8

+`6.283185`: 6.283188 -> $0006487f

binary files a/test/asm/underscore-in-numeric-literal.out.bin b/test/asm/underscore-in-numeric-literal.out.bin differ