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[libc][stdfix] Implement fxdivi functions (rdivi) #154914

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Merged
merged 14 commits into from
Oct 8, 2025
Merged

[libc][stdfix] Implement fxdivi functions (rdivi) #154914

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f54208e
[libc][stdfix] Implement fxdivi functions
bojle Aug 22, 2025
040e833
[libc][stdfix] add a couple more tests and error info for divi
bojle Aug 30, 2025
71d283b
[libc] add a few tests to handles edge cases with FRACT_{MIN/MAX}
bojle Sep 5, 2025
cfe5122
[libc] fix formatting for rdivi.cpp
bojle Sep 5, 2025
c614888
[libc] comments, remove extra iterations, and misc changes
bojle Sep 13, 2025
40cf04a
[libc] formatting
bojle Sep 25, 2025
744463c
[libc] INT_MIN handling
bojle Sep 26, 2025
f5ff751
[libc] formatting
bojle Sep 26, 2025
31bbc8b
[libc] multiply and divide by 2 when INT_MIN
bojle Sep 26, 2025
b631411
[libc] specially handle po2 cases
bojle Oct 5, 2025
73a93c3
[libc] add special handling for po2
bojle Oct 8, 2025
303dc94
[libc] use abs from algorithm.h
bojle Oct 8, 2025
07e1de8
[libc] add doc, fix func name case
bojle Oct 8, 2025
c2b4b99
[libc] TotalBits -> TOTAL_BITS
bojle Oct 8, 2025
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20 changes: 15 additions & 5 deletions libc/src/__support/fixed_point/fx_bits.h
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,8 @@

#include "fx_rep.h"

#include <stdio.h>

#ifdef LIBC_COMPILER_HAS_FIXED_POINT

namespace LIBC_NAMESPACE_DECL {
Expand Down Expand Up @@ -246,13 +248,21 @@ template <typename XType> LIBC_INLINE constexpr XType divi(int n, int d) {
}
bool result_is_negative = ((n < 0) != (d < 0));

unsigned int nv = static_cast<unsigned int>(n < 0 ? -n : n);
unsigned int dv = static_cast<unsigned int>(d < 0 ? -d : d);
unsigned int clz = cpp::countl_zero<unsigned int>(dv) - 1;
unsigned long int scaled_val = dv << clz;
int64_t n64 = static_cast<int64_t>(n);
int64_t d64 = static_cast<int64_t>(d);

uint64_t nv = static_cast<uint64_t>(n64 < 0 ? -n64 : n64);
uint64_t dv = static_cast<uint64_t>(d64 < 0 ? -d64 : d64);

if (d == INT_MIN) {
dv = dv - 1; // Two's complement
}

uint32_t clz = cpp::countl_zero<uint32_t>(static_cast<uint32_t>(dv)) - 1;
uint64_t scaled_val = dv << clz;
// Scale denominator to be in the range of [0.5,1]
FXBits<long accum> d_scaled{scaled_val};
unsigned long int scaled_val_n = nv << clz;
uint64_t scaled_val_n = nv << clz;
// Scale the numerator as much as the denominator to maintain correctness of
// the original equation
FXBits<long accum> n_scaled{scaled_val_n};
Expand Down
5 changes: 3 additions & 2 deletions libc/test/src/stdfix/DivITest.h
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Original file line number Diff line number Diff line change
Expand Up @@ -11,8 +11,6 @@
#include "src/__support/fixed_point/fx_rep.h"
#include "test/UnitTest/Test.h"

#include <stdio.h>

template <typename XType> XType get_epsilon() = delete;
template <> fract get_epsilon() { return FRACT_EPSILON; }
template <> unsigned fract get_epsilon() { return UFRACT_EPSILON; }
Expand Down Expand Up @@ -61,6 +59,9 @@ class DivITest : public LIBC_NAMESPACE::testing::Test {
EXPECT_LT(func(1, INT_MAX) - 0.r, epsilon);
// This results in 1.1739, which should be saturated to FRACT_MAX
EXPECT_EQ(func(27, 23), FRACT_MAX);

EXPECT_EQ(func(INT_MIN, 1), FRACT_MIN);
EXPECT_LT(func(1, INT_MIN) - 0.r, epsilon);
}
};

Expand Down
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