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Fix two bugs with RGBASM fixed-point math (#1388)

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- Fixed-point formulas are implemented using IEEE-754 floating-point
  internally, which could give infinity or NaN values whose conversion
  to fixed-point integer was platform-dependent.
- Formatting fixed-point $8000_0000 (INT32_MIN, -2147483648) was
  not putting the negative sign in front.
This commit is contained in:
Sylvie
2024-03-31 12:53:20 -04:00
committed by GitHub
parent 6b5248f15b
commit 9ab3446d1a
5 changed files with 36 additions and 12 deletions
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4
src/asm/fixpoint.cpp
View File

@@ -25,6 +25,10 @@ static double fix2double(int32_t i, int32_t q) {
}
static int32_t double2fix(double d, int32_t q) {
if (isnan(d))
return 0;
if (isinf(d))
return d < 0 ? INT32_MIN : INT32_MAX;
return (int32_t)round(d * pow(2.0, q));
}

22
src/asm/format.cpp
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@@ -4,6 +4,7 @@
#include <algorithm>
#include <inttypes.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@@ -153,10 +154,9 @@ void FormatSpec::appendNumber(std::string &str, uint32_t value) const {
char signChar = sign; // 0 or ' ' or '+'
if (useType == 'd' || useType == 'f') {
int32_t v = value;
if (v < 0 && v != INT32_MIN) {
if (int32_t v = value; v < 0) {
signChar = '-';
if (v != INT32_MIN)
value = -v;
}
}
@@ -194,16 +194,20 @@ void FormatSpec::appendNumber(std::string &str, uint32_t value) const {
useFracWidth = 255;
}
snprintf(
valueBuf, sizeof(valueBuf), "%.*f", (int)useFracWidth, value / fix_PrecisionFactor()
);
double fval = fabs(value / fix_PrecisionFactor());
snprintf(valueBuf, sizeof(valueBuf), "%.*f", (int)useFracWidth, fval);
} else if (useType == 'd') {
// Decimal numbers may be formatted with a '-' sign by `snprintf`, so `abs` prevents that,
// with a special case for `INT32_MIN` since `labs(INT32_MIN)` is UB. The sign will be
// printed later from `signChar`.
uint32_t uval = value != (uint32_t)INT32_MIN ? labs((int32_t)value) : value;
snprintf(valueBuf, sizeof(valueBuf), "%" PRIu32, uval);
} else {
char const *spec = useType == 'd' ? "%" PRId32
: useType == 'u' ? "%" PRIu32
char const *spec = useType == 'u' ? "%" PRIu32
: useType == 'X' ? "%" PRIX32
: useType == 'x' ? "%" PRIx32
: useType == 'o' ? "%" PRIo32
: "%" PRId32;
: "%" PRIu32;
snprintf(valueBuf, sizeof(valueBuf), spec, value);
}

8
test/asm/format-extremes.asm Normal file
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@@ -0,0 +1,8 @@
MACRO test
def v = \1
println "{#09x:v} = {#012o:v} = {#033b:v} = {u:v}U = {+d:v} = {+.16f:v}"
ENDM
test $7fff_ffff ; INT32_MAX
test $8000_0000 ; INT32_MIN
test $0000_0000 ; UINT32_MIN
test $ffff_ffff ; UINT32_MAX

4
test/asm/format-extremes.out Normal file
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@@ -0,0 +1,4 @@
$7fffffff = &17777777777 = %01111111111111111111111111111111 = 2147483647U = +2147483647 = +32767.9999847412109375
$80000000 = &20000000000 = %10000000000000000000000000000000 = 2147483648U = -2147483648 = -32768.0000000000000000
$00000000 = &00000000000 = %00000000000000000000000000000000 = 0U = +0 = +0.0000000000000000
$ffffffff = &37777777777 = %11111111111111111111111111111111 = 4294967295U = -1 = -0.0000152587890625

8
test/asm/math.asm
View File

@@ -19,14 +19,18 @@ ENDM
assert DIV(5.0, 2.0) == 2.5
assert DIV(-5.0, 2.0) == -2.5
assert DIV(-5.0, 0.0) == $8000_0000
assert DIV(5.0, 0.0) == $7fff_ffff ; +inf => INT32_MAX
assert DIV(-5.0, 0.0) == $8000_0000 ; -inf => INT32_MIN
assert DIV(0.0, 0.0) == $0000_0000 ; nan => 0
assert MUL(10.0, 0.5) == 5.0
assert MUL(10.0, 0.0) == 0.0
assert FMOD(5.0, 2.0) == 1.0
assert FMOD(-5.0, 2.0) == -1.0
assert FMOD(-5.0, 0.0) == $8000_0000
assert FMOD(5.0, 0.0) == 0 ; nan
assert FMOD(-5.0, 0.0) == 0 ; nan
assert FMOD(0.0, 0.0) == 0 ; nan
assert POW(10.0, 2.0) == 100.0
assert POW(100.0, 0.5) == 10.0