SubC

Applicability

Product	Supported
Atlas 350 Accelerator Card	√
Atlas A3 training product/Atlas A3 inference product	x
Atlas A2 training product/Atlas A2 inference product	x
Atlas 200I/500 A2 inference product	x
Atlas inference product AI Core	x
Atlas inference product Vector Core	x
Atlas training product	x

Function Usage

Performs subtraction between the source operands srcReg0 and srcReg1 and the carry data carrySrc element-wise based on mask and writes the result to the destination operand dstReg. If the borrowing result is generated when subtraction is performed between srcReg0, srcReg1, and carrySrc, the least significant bit of every four bits in the corresponding position of MaskReg carry is written as 0. Otherwise, it is written as 1. The formula is as follows:

$\text{[math]}$

Examples:

**Table 1** Examples
Data Type	Borrowing	Examples
int32_t	No	a_i = 5, b_i = 2, carrySrc_i = 1 dst_i = a_i - b_i - carrySrc_i = 2 Write 1 to the least significant bit of every four bits in the corresponding position in carryp: carry_i = 1
int32_t	Yes	a_i = 5, b_i = -7, carrySrc_i = 1 dst_i = a_i - b_i - carrySrc_i = 11 Write 0 to the least significant bit of every four bits in the corresponding position in carryp: carry_i = 0
uint32_t	No	a_i = 5, b_i = 2, carrySrc_i = 1 dst_i = a_i - b_i - carrySrc_i = 2 Write 1 to the least significant bit of every four bits in the corresponding position in carryp: carry_i = 1
uint32_t	Yes	a_i = 5, b_i = 7, carrySrc_i = 1 dst_i = a_i - b_i - carrySrc_i = -3 Write 0 to the least significant bit of every four bits in the corresponding position in carryp: carry_i = 0

Prototype

template <typename T = DefaultType, typename U>
__simd_callee__ inline void SubC(MaskReg& carry, U& dstReg, U& srcReg0, U& srcReg1, MaskReg& carrySrc, MaskReg& mask)

Parameters

**Table 2** Parameters in the template
Parameter	Description
T	Data type of the vector destination operand and source operand. For the Atlas 350 Accelerator Card, the supported data types are uint32_t and int32_t.
U	RegTensor type of the destination operand, for example, RegTensor<half>. It is automatically inferred by the compiler and does not need to be specified.

**Table 3** Parameters
Parameter	Input/Output	Description
dstReg	Output	Destination operand. The type is RegTensor.
srcReg0	Input	Source operand. The type is RegTensor. The source and destination operands must have the same data type.
srcReg1	Input	Source operand. The type is RegTensor. The source and destination operands must have the same data type.
carrySrc	Input	Source operand. Input carry value. The type is MaskReg.
carry	Output	Destination operand. Output carry value. The type is MaskReg.
mask	Input	Valid indication of the source operand element operation. For details, see MaskReg.

Returns

None

Restrictions

None

Examples

template <typename T>
__simd_vf__ inline void SubC(__ubuf__ T* dst0Addr, __ubuf__ T* dst1Addr, __ubuf__ T* src0Addr, __ubuf__ T* src1Addr, uint32_t count, uint16_t repeatTimes, uint32_t oneRepeatSize){
    
    AscendC::Reg::RegTensor<T> srcReg0;
    AscendC::Reg::RegTensor<T> srcReg1;
    AscendC::Reg::RegTensor<T> dstReg0;
    AscendC::Reg::MaskReg mask; 
    AscendC::Reg::MaskReg maskZero = AscendC::Reg::CreateMask<T, AscendC::Reg::MaskPattern::ALLF>();
    AscendC::Reg::MaskReg carry = AscendC::Reg::CreateMask<uint8_t>();
    for (uint16_t i = 0; i < repeatTimes; i++) {
        mask = AscendC::Reg::UpdateMask<T>(count);
        AscendC::Reg::LoadAlign(srcReg0, src0Addr + i * oneRepeatSize);
        AscendC::Reg::LoadAlign(srcReg1, src1Addr + i * oneRepeatSize);
        AscendC::Reg::SubC(carry, dstReg0, srcReg0, srcReg1, maskZero, mask);
        // 8*4B=32B align
        AscendC::Reg::StoreAlign<uint32_t, AscendC::Reg::MaskDist::DIST_NORM>((__ubuf__ uint32_t*)dst1Addr + i * 8, carry);
        AscendC::Reg::StoreAlign(dst0Addr + i * oneRepeatSize, dstReg0, mask);
    }
}

Parent topic: Basic Arithmetic