science

MOVAPD

MOVAPD is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand MOVAPD rather than just read about it. In short: In the x86 assembly programming language, MOVAPD is the name for a specific action performable by modern x86 processors with 2nd-generation Streaming SIMD Extensions (SSE2). This action involves copying a pair of numbers to temporary space in the processor for use in other computations.

Key takeaways

MOVAPD belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect MOVAPD to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of MOVAPD from memory before moving on to harder problems.

Reference excerpt

In the x86 assembly programming language, MOVAPD is the name for a specific action performable by modern x86 processors with 2nd-generation Streaming SIMD Extensions (SSE2). This action involves copying a pair of numbers to temporary space in the processor for use in other computations. MOVAPD is one of the fastest ways to accomplish this effect - it is faster than the comparable instruction MOVSD. Specifically, MOVAPD causes a 16-byte-aligned packed-doubles source to be copied to an XMM register or a 16-byte memory region.

Usage

The source operand can be either an XMM register (xmm2) or a memory address (m128). The destination operand can be either an XMM register (xmm1) or a memory address (m128). Note, however, that the source and destination operands cannot both be memory addresses.

Potential Exceptions If a memory address operand is not 16-byte-aligned, a general protection exception (#GP) will be raised. This can cause strange interoperability bugs when ordinary code calls an external code that was compiled with the assumption of a 16-byte-aligned stack frame boundary.

References gcc info documentation Intel 64 and IA-32 Architectures Optimization Reference Manual, November, 2006. Intel 64 and IA-32 Architectures Software Developer's Manual Volume 2A: Instruction Set Reference, A-M, November, 2006.

See also MOVAPS/MOVAPD MOVDDUP MOVHLPS MOVHPS/MOVHPD MOVLHPS MOVLPS/MOVLPD MOVMSKPS/MOVMSKPD MOVNTPS MOVSHDUP MOVSLDUP MOVSS/MOVSD MOVUPS/MOVUPD

x86 instruction listings

Worked examples

Example 1 — a first encounter with MOVAPD

Start with the simplest possible case. Write down what MOVAPD claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to MOVAPD before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about MOVAPD ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of MOVAPD

In research: MOVAPD appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses MOVAPD in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: MOVAPD is common in secondary-school and first-year university syllabi. It links to neighbouring topics Programming language topic stubs, X86 instructions, so understanding it makes those chapters shorter.
In everyday life: Look for MOVAPD outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study MOVAPD in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what MOVAPD means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain MOVAPD out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is MOVAPD in simple terms?

Why does MOVAPD matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study MOVAPD?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on MOVAPD.