Skip to content

Commit

Permalink
[vm/simarm] Fix VRECPS/VRSQRTSQS instruction implementation.
Browse files Browse the repository at this point in the history 
This instruction handles 0.0 and infinity operands
specially because otherwise it produces NaN where it
should produce appropriate infinity or zero.

Fixes dart-lang#24399
Fixes dart-lang#26675
Fixes dart-lang#38844

This relands commit 3da9c34

Change-Id: I116cea3b6c27b5dc16741f9652fbbb9a3ec1194e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/121705
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>
  • Loading branch information
@mraleph
mraleph authored and commit-bot@chromium.org committed Oct 15, 2019
1 parent 32ff830 commit f297516
Showing 1 changed file with 50 additions and 93 deletions.
143 changes: 50 additions & 93 deletions assembler_arm_test.cc
View file
Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,54 @@
namespace dart {
namespace compiler {

TEST_CASE(ReciprocalOps) {
EXPECT_EQ(true, isinf(ReciprocalEstimate(-0.0f)));
EXPECT_EQ(true, signbit(ReciprocalEstimate(-0.0f)));
EXPECT_EQ(true, isinf(ReciprocalEstimate(0.0f)));
EXPECT_EQ(true, !signbit(ReciprocalEstimate(0.0f)));
EXPECT_EQ(true, isnan(ReciprocalEstimate(NAN)));

#define AS_UINT32(v) (bit_cast<uint32_t, float>(v))
#define EXPECT_BITWISE_EQ(a, b) EXPECT_EQ(AS_UINT32(a), AS_UINT32(b))

EXPECT_BITWISE_EQ(0.0f, ReciprocalEstimate(kPosInfinity));
EXPECT_BITWISE_EQ(-0.0f, ReciprocalEstimate(kNegInfinity));
EXPECT_BITWISE_EQ(2.0f, ReciprocalStep(0.0f, kPosInfinity));
EXPECT_BITWISE_EQ(2.0f, ReciprocalStep(0.0f, kNegInfinity));
EXPECT_BITWISE_EQ(2.0f, ReciprocalStep(-0.0f, kPosInfinity));
EXPECT_BITWISE_EQ(2.0f, ReciprocalStep(-0.0f, kNegInfinity));
EXPECT_BITWISE_EQ(2.0f, ReciprocalStep(kPosInfinity, 0.0f));
EXPECT_BITWISE_EQ(2.0f, ReciprocalStep(kNegInfinity, 0.0f));
EXPECT_BITWISE_EQ(2.0f, ReciprocalStep(kPosInfinity, -0.0f));
EXPECT_BITWISE_EQ(2.0f, ReciprocalStep(kNegInfinity, -0.0f));
EXPECT_EQ(true, isnan(ReciprocalStep(NAN, 1.0f)));
EXPECT_EQ(true, isnan(ReciprocalStep(1.0f, NAN)));

EXPECT_EQ(true, isnan(ReciprocalSqrtEstimate(-1.0f)));
EXPECT_EQ(true, isnan(ReciprocalSqrtEstimate(kNegInfinity)));
EXPECT_EQ(true, isnan(ReciprocalSqrtEstimate(-1.0f)));
EXPECT_EQ(true, isinf(ReciprocalSqrtEstimate(-0.0f)));
EXPECT_EQ(true, signbit(ReciprocalSqrtEstimate(-0.0f)));
EXPECT_EQ(true, isinf(ReciprocalSqrtEstimate(0.0f)));
EXPECT_EQ(true, !signbit(ReciprocalSqrtEstimate(0.0f)));
EXPECT_EQ(true, isnan(ReciprocalSqrtEstimate(NAN)));
EXPECT_BITWISE_EQ(0.0f, ReciprocalSqrtEstimate(kPosInfinity));

EXPECT_BITWISE_EQ(1.5f, ReciprocalSqrtStep(0.0f, kPosInfinity));
EXPECT_BITWISE_EQ(1.5f, ReciprocalSqrtStep(0.0f, kNegInfinity));
EXPECT_BITWISE_EQ(1.5f, ReciprocalSqrtStep(-0.0f, kPosInfinity));
EXPECT_BITWISE_EQ(1.5f, ReciprocalSqrtStep(-0.0f, kNegInfinity));
EXPECT_BITWISE_EQ(1.5f, ReciprocalSqrtStep(kPosInfinity, 0.0f));
EXPECT_BITWISE_EQ(1.5f, ReciprocalSqrtStep(kNegInfinity, 0.0f));
EXPECT_BITWISE_EQ(1.5f, ReciprocalSqrtStep(kPosInfinity, -0.0f));
EXPECT_BITWISE_EQ(1.5f, ReciprocalSqrtStep(kNegInfinity, -0.0f));
EXPECT_EQ(true, isnan(ReciprocalSqrtStep(NAN, 1.0f)));
EXPECT_EQ(true, isnan(ReciprocalSqrtStep(1.0f, NAN)));

#undef AS_UINT32
#undef EXPECT_BITWISE_EQ
}

#define __ assembler->

ASSEMBLER_TEST_GENERATE(Simple, assembler) {
Expand Down Expand Up @@ -3430,43 +3478,6 @@ ASSEMBLER_TEST_RUN(Vmaxqs, test) {
}
}

// This is the same function as in the Simulator.
static float arm_recip_estimate(float a) {
// From the ARM Architecture Reference Manual A2-85.
if (isinf(a) || (fabs(a) >= exp2f(126)))
return 0.0;
else if (a == 0.0)
return kPosInfinity;
else if (isnan(a))
return a;

uint32_t a_bits = bit_cast<uint32_t, float>(a);
// scaled = '0011 1111 1110' : a<22:0> : Zeros(29)
uint64_t scaled = (static_cast<uint64_t>(0x3fe) << 52) |
((static_cast<uint64_t>(a_bits) & 0x7fffff) << 29);
// result_exp = 253 - UInt(a<30:23>)
int32_t result_exp = 253 - ((a_bits >> 23) & 0xff);
ASSERT((result_exp >= 1) && (result_exp <= 252));

double scaled_d = bit_cast<double, uint64_t>(scaled);
ASSERT((scaled_d >= 0.5) && (scaled_d < 1.0));

// a in units of 1/512 rounded down.
int32_t q = static_cast<int32_t>(scaled_d * 512.0);
// reciprocal r.
double r = 1.0 / ((static_cast<double>(q) + 0.5) / 512.0);
// r in units of 1/256 rounded to nearest.
int32_t s = static_cast<int32_t>(256.0 * r + 0.5);
double estimate = static_cast<double>(s) / 256.0;
ASSERT((estimate >= 1.0) && (estimate <= (511.0 / 256.0)));

// result = sign : result_exp<7:0> : estimate<51:29>
int32_t result_bits =
(a_bits & 0x80000000) | ((result_exp & 0xff) << 23) |
((bit_cast<uint64_t, double>(estimate) >> 29) & 0x7fffff);
return bit_cast<float, int32_t>(result_bits);
}

ASSEMBLER_TEST_GENERATE(Vrecpeqs, assembler) {
if (TargetCPUFeatures::neon_supported()) {
__ LoadSImmediate(S4, 147.0);
Expand All @@ -3483,7 +3494,7 @@ ASSEMBLER_TEST_RUN(Vrecpeqs, test) {
if (TargetCPUFeatures::neon_supported()) {
typedef float (*Vrecpeqs)() DART_UNUSED;
float res = EXECUTE_TEST_CODE_FLOAT(Vrecpeqs, test->entry());
EXPECT_FLOAT_EQ(arm_recip_estimate(147.0), res, 0.0001f);
EXPECT_FLOAT_EQ(ReciprocalEstimate(147.0), res, 0.0001f);
}
}

Expand Down Expand Up @@ -3540,60 +3551,6 @@ ASSEMBLER_TEST_RUN(Reciprocal, test) {
}
}

static float arm_reciprocal_sqrt_estimate(float a) {
// From the ARM Architecture Reference Manual A2-87.
if (isinf(a) || (fabs(a) >= exp2f(126)))
return 0.0;
else if (a == 0.0)
return kPosInfinity;
else if (isnan(a))
return a;

uint32_t a_bits = bit_cast<uint32_t, float>(a);
uint64_t scaled;
if (((a_bits >> 23) & 1) != 0) {
// scaled = '0 01111111101' : operand<22:0> : Zeros(29)
scaled = (static_cast<uint64_t>(0x3fd) << 52) |
((static_cast<uint64_t>(a_bits) & 0x7fffff) << 29);
} else {
// scaled = '0 01111111110' : operand<22:0> : Zeros(29)
scaled = (static_cast<uint64_t>(0x3fe) << 52) |
((static_cast<uint64_t>(a_bits) & 0x7fffff) << 29);
}
// result_exp = (380 - UInt(operand<30:23>) DIV 2;
int32_t result_exp = (380 - ((a_bits >> 23) & 0xff)) / 2;

double scaled_d = bit_cast<double, uint64_t>(scaled);
ASSERT((scaled_d >= 0.25) && (scaled_d < 1.0));

double r;
if (scaled_d < 0.5) {
// range 0.25 <= a < 0.5

// a in units of 1/512 rounded down.
int32_t q0 = static_cast<int32_t>(scaled_d * 512.0);
// reciprocal root r.
r = 1.0 / sqrt((static_cast<double>(q0) + 0.5) / 512.0);
} else {
// range 0.5 <= a < 1.0

// a in units of 1/256 rounded down.
int32_t q1 = static_cast<int32_t>(scaled_d * 256.0);
// reciprocal root r.
r = 1.0 / sqrt((static_cast<double>(q1) + 0.5) / 256.0);
}
// r in units of 1/256 rounded to nearest.
int32_t s = static_cast<int>(256.0 * r + 0.5);
double estimate = static_cast<double>(s) / 256.0;
ASSERT((estimate >= 1.0) && (estimate <= (511.0 / 256.0)));

// result = 0 : result_exp<7:0> : estimate<51:29>
int32_t result_bits =
((result_exp & 0xff) << 23) |
((bit_cast<uint64_t, double>(estimate) >> 29) & 0x7fffff);
return bit_cast<float, int32_t>(result_bits);
}

ASSEMBLER_TEST_GENERATE(Vrsqrteqs, assembler) {
if (TargetCPUFeatures::neon_supported()) {
__ LoadSImmediate(S4, 147.0);
Expand All @@ -3611,7 +3568,7 @@ ASSEMBLER_TEST_RUN(Vrsqrteqs, test) {
if (TargetCPUFeatures::neon_supported()) {
typedef float (*Vrsqrteqs)() DART_UNUSED;
float res = EXECUTE_TEST_CODE_FLOAT(Vrsqrteqs, test->entry());
EXPECT_FLOAT_EQ(arm_reciprocal_sqrt_estimate(147.0), res, 0.0001f);
EXPECT_FLOAT_EQ(ReciprocalSqrtEstimate(147.0), res, 0.0001f);
}
}

Expand Down

0 comments on commit f297516

Please sign in to comment.