SIMD

x86

• Terminology:
  • half precision: 16-bit IEEE 754 floating-point (bias-15) (IEEE 754 2008 binary16)
  • single: 32-bit IEEE 754 floating-point (bias-127) (IEEE 754 2008 binary32)
  • double: 64-bit IEEE 754 floating-point (bias-1023) (IEEE 754 2008 binary64)
  • long double: 80-bit "double extended" IEEE 754-1985 floating-point (bias-16383)
    • not an actual SIMD type, but an artifact of x87
  • word: 32-bit two's complement integer
  • doubleword, dword: 64-bit two's complement integer
• These do not necessarily map to the C data types of the same name, for any given compiler!

Future

• AVX (Advanced Vector eXtensions) -- to be introduced on Intel's Sandy Bridge (2010) and AMD's Bulldozer (2011), and implemented within the VEX coding scheme
• The FMA instruction set extension to x86 should hit around 2011, providing floating-point fused multiply-add
  • AMD appears to call this FMA4, part of what was SSE5

SSE5 (AMD)

• Unimplemented extensions competing with SSE4, encoded using a method incompatible with VEX
• Withdrawn, converted into VEX-compatible encodings, and split into:
  • FMA4: Fused floating-point multiply-add (compare Intel's FMA)
  • XOP: Fused integer multiply-add, byte permutations, shifts, rotates, integer vector horizontal operations (compare Intel's SSE4)
  • CVT16: Half-precision conversion

SSE4 (Intel)

SSE4.1

DPPD instruction dataflow

• dpps -- dot product of two vectors having four single components each
• dppd -- dot product of two vectors having two double components each
• insertps

SSE3

• movddup -- move a double from a 8-byte-aligned memory location or lower half of XMM register to upper half, then duplicate upper half to lower half

SSSE3

• pmaddwd -- multiply packed words, then horizontally sum pairs, accumulating into doublewords

SSE2

• movapd -- move two packed doubles from a 16-byte-aligned memory location to XMM registers, or vice versa, or between two XMM registers.
  • movupd -- movapd safe for unaligned memory references, with far inferior performance.
• mulpd -- multiply two packed doubles. the multiplier is a 16-byte-aligned memory location or XMM register. the target XMM register serves as the multiplicand.
• addpd -- add two packed doubles. the addend is a 16-byte-aligned memory location or XMM register. the target XMM register serves as the augend.

SSE

• movaps -- move four packed singles from a 16-byte-aligned memory location to XMM registers, or vice versa, or between two XMM registers.
  • movups -- movaps safe for unaligned memory references, with far inferior performance.
• mulps -- multiply four packed singles. the multiplier is a 16-byte-aligned memory location or XMM register. the target XMM register serves as the multiplicand.
• addps -- add four packed singles. the addend is a 16-byte-aligned memory location or XMM register. the target XMM register serves as the augend.

Other Architectures

• PowerPC implements AltiVec
• SPARC implements VIS, the Visual Instruction Set
• PA-RISC implements MAX, the Multimedia Acceleration eXtensions
• ARM implements NEON
• Alpha implemented MVI, the Motion Video Instructions
• SWAR: SIMD Within a Register (bit-parallel methods)

See Also

• "Why no FMA in AVX in Sandy Bridge?", Intel Developers Forum
• SSE5 guide at AMD
• 2007-04-19 post to http://virtualdub.org, "SSE4 finally adds dot products"