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Type:
Bug
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Resolution: Unresolved
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Priority:
Low
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Code Generation Tools
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CODEGEN-8400
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default
The attached main.cpp has these lines ...
int main()
{
const float a = 0.0f;
const float b = -0.0f;
const float c = std::copysign(0.0f, -1.0f);
std::printf("%08x\n", byte_cast<uint32_t>(a)); // expected: 0x00000000, actual: 0x00000000
std::printf("%08x\n", byte_cast<uint32_t>(b)); // expected: 0x80000000, actual: 0x00000000
std::printf("%08x\n", byte_cast<uint32_t>(c)); // expected: 0x80000000, actual: 0x80000000
assert(std::signbit(a) == false); // ok
assert(std::signbit(b) == true); // fails!
assert(std::signbit(c) == true); // ok
}
Build it ...
"C:/ti/compilers/ti-cgt-arm_18.12.3.LTS/bin/armcl" -mv7M4 --code_state=16 --float_support=none -me -O3 --opt_for_speed=4 --include_path="C:/Users/a0321429/workspace_v10_1/negative_zero_test_cc1352r1" --include_path="C:/ti/compilers/ti-cgt-arm_18.12.3.LTS/include" -g --diag_warning=225 --diag_wrap=off --display_error_number --abi=eabi --ramfunc=off --src_interlist --preproc_with_compile --preproc_dependency="main.d_raw" "../main.cpp"
When the code is executed, this is the output ...
00000000 00000000 80000000 Assertion failed, (std::signbit(b) == true), file ../main.cpp, line 25
The second line should be 80000000. No assertion should fail.
Here is part of the assembly output in main.asm ...
;** 18 ----------------------- a = 0.0F;
;** 19 ----------------------- b = -0.0F;
;* 1080 ----------------------- c = copysignf(C$11 = 0.0F, -1.0F); // [1]
;** 12 ----------------------- memcpy(&result, &a, 4u); // [3]
;** 21 ----------------------- printf[VA](C$12 = "%08x\n", (unsigned)result);
;** 12 ----------------------- memcpy(&result, &b, 4u); // [3]
;** 22 ----------------------- printf[VA](C$12, (unsigned)result);
;** 12 ----------------------- memcpy(&result, &c, 4u); // [3]
;** 23 ----------------------- printf[VA](C$12, (unsigned)result);
;** 24 ----------------------- assert((_ftoi(C$11)&0x80000000u) == 0);
PUSH {V1, V2, LR} ; [DPU_V7M3_PIPE]
.dwcfi cfa_offset, 12
.dwcfi save_reg_to_mem, 14, -4
.dwcfi save_reg_to_mem, 5, -8
.dwcfi save_reg_to_mem, 4, -12
.dwpsn file "../main.cpp",line 18,column 19,is_stmt,isa 1
MOVS V1, #0 ; [DPU_V7M3_PIPE] |18|
.dwpsn file "C:/ti/compilers/ti-cgt-arm_18.12.3.LTS/include/libcxx/math.h",line 1080,column 3,is_stmt,isa 1
MOVS A2, #0 ; [DPU_V7M3_PIPE] |1080|
SUB SP, SP, #28 ; [DPU_V7M3_PIPE]
.dwcfi cfa_offset, 40
.dwpsn file "../main.cpp",line 18,column 19,is_stmt,isa 1
MOVT V1, #0 ; [DPU_V7M3_PIPE] |18|
.dwpsn file "C:/ti/compilers/ti-cgt-arm_18.12.3.LTS/include/libcxx/math.h",line 1080,column 3,is_stmt,isa 1
MOVT A2, #49024 ; [DPU_V7M3_PIPE] |1080|
.dwpsn file "../main.cpp",line 18,column 19,is_stmt,isa 1
STR V1, [SP, #0] ; [DPU_V7M3_PIPE] |18|
.dwpsn file "C:/ti/compilers/ti-cgt-arm_18.12.3.LTS/include/libcxx/math.h",line 1080,column 3,is_stmt,isa 1
MOV A1, V1 ; [DPU_V7M3_PIPE] |1080|
.dwpsn file "../main.cpp",line 19,column 19,is_stmt,isa 1
STR V1, [SP, #4] ; [DPU_V7M3_PIPE] |19|
The last STR should store the value 0x80000000 to that memory location on the stack. But it stores 0 instead.
Also attached is a CCS project which runs on a LAUNCHXL-CC1352R1.
