Commit 4bd4ee07 by Christophe Lyon Committed by Aurelien Jarno

### target-arm: Fix rounding constant addition for Neon shifts

```

Handle cases where adding the rounding constant could overflow in Neon
shift instructions: VRSHR, VRSRA, VQRSHRN, VQRSHRUN, VRSHRN.
Signed-off-by: Christophe Lyon <christophe.lyon@st.com>
[peter.maydell@linaro.org: fix handling of large shifts in rshl_s32,
calculate signed saturated value as other functions do.]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>```
parent d68a6f3a
 ... ... @@ -558,9 +558,28 @@ uint64_t HELPER(neon_shl_s64)(uint64_t valop, uint64_t shiftop) }} while (0) NEON_VOP(rshl_s8, neon_s8, 4) NEON_VOP(rshl_s16, neon_s16, 2) NEON_VOP(rshl_s32, neon_s32, 1) #undef NEON_FN /* The addition of the rounding constant may overflow, so we use an * intermediate 64 bits accumulator. */ uint32_t HELPER(neon_rshl_s32)(uint32_t valop, uint32_t shiftop) { int32_t dest; int32_t val = (int32_t)valop; int8_t shift = (int8_t)shiftop; if ((shift >= 32) || (shift <= -32)) { dest = 0; } else if (shift < 0) { int64_t big_dest = ((int64_t)val + (1 << (-1 - shift))); dest = big_dest >> -shift; } else { dest = val << shift; } return dest; } /* Handling addition overflow with 64 bits inputs values is more * tricky than with 32 bits values. */ uint64_t HELPER(neon_rshl_s64)(uint64_t valop, uint64_t shiftop) { int8_t shift = (int8_t)shiftop; ... ... @@ -574,7 +593,16 @@ uint64_t HELPER(neon_rshl_s64)(uint64_t valop, uint64_t shiftop) val++; val >>= 1; } else if (shift < 0) { val = (val + ((int64_t)1 << (-1 - shift))) >> -shift; val >>= (-shift - 1); if (val == INT64_MAX) { /* In this case, it means that the rounding constant is 1, * and the addition would overflow. Return the actual * result directly. */ val = 0x4000000000000000LL; } else { val++; val >>= 1; } } else { val <<= shift; } ... ... @@ -596,9 +624,29 @@ uint64_t HELPER(neon_rshl_s64)(uint64_t valop, uint64_t shiftop) }} while (0) NEON_VOP(rshl_u8, neon_u8, 4) NEON_VOP(rshl_u16, neon_u16, 2) NEON_VOP(rshl_u32, neon_u32, 1) #undef NEON_FN /* The addition of the rounding constant may overflow, so we use an * intermediate 64 bits accumulator. */ uint32_t HELPER(neon_rshl_u32)(uint32_t val, uint32_t shiftop) { uint32_t dest; int8_t shift = (int8_t)shiftop; if (shift >= 32 || shift < -32) { dest = 0; } else if (shift == -32) { dest = val >> 31; } else if (shift < 0) { uint64_t big_dest = ((uint64_t)val + (1 << (-1 - shift))); dest = big_dest >> -shift; } else { dest = val << shift; } return dest; } /* Handling addition overflow with 64 bits inputs values is more * tricky than with 32 bits values. */ uint64_t HELPER(neon_rshl_u64)(uint64_t val, uint64_t shiftop) { int8_t shift = (uint8_t)shiftop; ... ... @@ -607,9 +655,17 @@ uint64_t HELPER(neon_rshl_u64)(uint64_t val, uint64_t shiftop) } else if (shift == -64) { /* Rounding a 1-bit result just preserves that bit. */ val >>= 63; } if (shift < 0) { val = (val + ((uint64_t)1 << (-1 - shift))) >> -shift; val >>= -shift; } else if (shift < 0) { val >>= (-shift - 1); if (val == UINT64_MAX) { /* In this case, it means that the rounding constant is 1, * and the addition would overflow. Return the actual * result directly. */ val = 0x8000000000000000ULL; } else { val++; val >>= 1; } } else { val <<= shift; } ... ... @@ -784,14 +840,43 @@ uint64_t HELPER(neon_qshlu_s64)(CPUState *env, uint64_t valop, uint64_t shiftop) }} while (0) NEON_VOP_ENV(qrshl_u8, neon_u8, 4) NEON_VOP_ENV(qrshl_u16, neon_u16, 2) NEON_VOP_ENV(qrshl_u32, neon_u32, 1) #undef NEON_FN /* The addition of the rounding constant may overflow, so we use an * intermediate 64 bits accumulator. */ uint32_t HELPER(neon_qrshl_u32)(CPUState *env, uint32_t val, uint32_t shiftop) { uint32_t dest; int8_t shift = (int8_t)shiftop; if (shift < 0) { uint64_t big_dest = ((uint64_t)val + (1 << (-1 - shift))); dest = big_dest >> -shift; } else { dest = val << shift; if ((dest >> shift) != val) { SET_QC(); dest = ~0; } } return dest; } /* Handling addition overflow with 64 bits inputs values is more * tricky than with 32 bits values. */ uint64_t HELPER(neon_qrshl_u64)(CPUState *env, uint64_t val, uint64_t shiftop) { int8_t shift = (int8_t)shiftop; if (shift < 0) { val = (val + (1 << (-1 - shift))) >> -shift; val >>= (-shift - 1); if (val == UINT64_MAX) { /* In this case, it means that the rounding constant is 1, * and the addition would overflow. Return the actual * result directly. */ val = 0x8000000000000000ULL; } else { val++; val >>= 1; } } else { \ uint64_t tmp = val; val <<= shift; ... ... @@ -817,22 +902,52 @@ uint64_t HELPER(neon_qrshl_u64)(CPUState *env, uint64_t val, uint64_t shiftop) }} while (0) NEON_VOP_ENV(qrshl_s8, neon_s8, 4) NEON_VOP_ENV(qrshl_s16, neon_s16, 2) NEON_VOP_ENV(qrshl_s32, neon_s32, 1) #undef NEON_FN /* The addition of the rounding constant may overflow, so we use an * intermediate 64 bits accumulator. */ uint32_t HELPER(neon_qrshl_s32)(CPUState *env, uint32_t valop, uint32_t shiftop) { int32_t dest; int32_t val = (int32_t)valop; int8_t shift = (int8_t)shiftop; if (shift < 0) { int64_t big_dest = ((int64_t)val + (1 << (-1 - shift))); dest = big_dest >> -shift; } else { dest = val << shift; if ((dest >> shift) != val) { SET_QC(); dest = (val >> 31) ^ ~SIGNBIT; } } return dest; } /* Handling addition overflow with 64 bits inputs values is more * tricky than with 32 bits values. */ uint64_t HELPER(neon_qrshl_s64)(CPUState *env, uint64_t valop, uint64_t shiftop) { int8_t shift = (uint8_t)shiftop; int64_t val = valop; if (shift < 0) { val = (val + (1 << (-1 - shift))) >> -shift; val >>= (-shift - 1); if (val == INT64_MAX) { /* In this case, it means that the rounding constant is 1, * and the addition would overflow. Return the actual * result directly. */ val = 0x4000000000000000ULL; } else { val++; val >>= 1; } } else { int64_t tmp = val;; int64_t tmp = val; val <<= shift; if ((val >> shift) != tmp) { SET_QC(); val = tmp >> 31; val = (tmp >> 63) ^ ~SIGNBIT64; } } return val; ... ...
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