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base: improve floating point output

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Fixes #2876
This commit is contained in:
Christian Prochaska 2018-12-10 14:18:37 +01:00 committed by Norman Feske
parent 3347d08b79
commit a5547e5b1d
4 changed files with 25 additions and 7 deletions
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1
repos/base/recipes/pkg/test-log/runtime
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@ -9,6 +9,7 @@
[init -> test-log] invalid hex range: [f8,08) (overflow!)
[init -> test-log] negative hex char: 0xfe
[init -> test-log] positive hex char: 0x02
[init -> test-log] floating point: 1.70
[init -> test-log] multiarg string: "parent -> child.7"
[init -> test-log] String(Hex(3)): 0x3
[init -> test-log] Very long messages:

1
repos/base/run/log.run
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@ -36,6 +36,7 @@ compare_output_to {
[init -> test-log] invalid hex range: [f8,08) (overflow!)
[init -> test-log] negative hex char: 0xfe
[init -> test-log] positive hex char: 0x02
[init -> test-log] floating point: 1.70
[init -> test-log] multiarg string: "parent -> child.7"
[init -> test-log] String(Hex(3)): 0x3
[init -> test-log] Very long messages:

28
repos/base/src/include/base/internal/output.h
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@ -114,13 +114,27 @@ static inline void out_float(T value, unsigned base, unsigned length, OUT_CHAR_F
{
using namespace Genode;
/*
* If the compiler decides to move a value from the FPU to the stack and
* back, the value can slightly change because of different encodings. This
* can cause problems if the value is assumed to stay the same in a chain
* of calculations. For example, if casting 6.999 to int results in 6, this
* number 6 needs to be subtracted from 6.999 in the next step and not from
* 7 after an unexpected conversion, otherwise the next cast for a decimal
* place would result in 10 instead of 9.
* By storing the value in a volatile variable, the conversion step between
* FPU and stack happens in a more deterministic way, which gives more
* consistent results with this function.
*/
T volatile volatile_value = value;
/* set flag if value is negative */
int neg = value < 0 ? 1 : 0;
int neg = volatile_value < 0 ? 1 : 0;
/* get absolute value */
value = value < 0 ? -value : value;
volatile_value = volatile_value < 0 ? -volatile_value : volatile_value;
uint64_t integer = (uint64_t)value;
uint64_t integer = (uint64_t)volatile_value;
if (neg)
out_char('-');
@ -130,14 +144,14 @@ static inline void out_float(T value, unsigned base, unsigned length, OUT_CHAR_F
if (length) {
do {
value -= integer;
value = value*base;
volatile_value -= integer;
volatile_value = volatile_value*base;
integer = (int64_t)value;
integer = (int64_t)volatile_value;
out_char(ascii(integer));
length--;
} while (length && (value > 0.0));
} while (length && (volatile_value > 0.0));
}
}

2
repos/base/src/test/log/main.cc
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@ -28,6 +28,8 @@ void Component::construct(Genode::Env &env)
log("negative hex char: ", Hex((char)-2LL, Hex::PREFIX, Hex::PAD));
log("positive hex char: ", Hex((char) 2LL, Hex::PREFIX, Hex::PAD));
log("floating point: ", 1700.0 / 1000);
typedef String<128> Label;
log("multiarg string: ", Label(Char('"'), "parent -> child.", 7, Char('"')));