Type Sizes

Once you know how to size the 4 basic types, you can size any type in Numstore. If you haven't yet, read the type system first - it walks through each rule.

The size rules

Practice problems

ns.to_dtype(...).itemsize will check your answers.

1. What is the element size of struct { a u16, b i64, c f32 }?
2. What is the element size of union { a u16, b i64, c f32 }?
3. What is the element size of [10][20] u32?
4. What is the element size of [100] struct { x f32, y f32, z f32 }?
5. What is the element size of struct { id u64, samples [8] cf64 }?
6. What is the element size of [12][256][256] struct { r u8, g u8, b u8 }?
7. In a [4][4] f32, what byte offset is element [2][3]?
8. What is the element size of struct { tag u8, payload union { a f64, b [2] u32 } }?

Answers

1. 2 + 8 + 4 = 14 bytes.
2. max(2, 8, 4) = 8 bytes.
3. 10 x 20 x 4 = 800 bytes.
4. struct is 12, so 100 x 12 = 1,200 bytes.
5. cf64 is 8 bytes -> samples is 8 x 8 = 64, plus id at 8 -> 72 bytes.
6. struct is 3, array is 12 x 256 x 256 = 786,432 -> 2,359,296 bytes.
7. (2 x 4 + 3) x 4 = 11 x 4 = 44 bytes.
8. union is max(8, 2 x 4) = 8, plus tag at 1 -> 9 bytes.

Check the answers

>>> import pynumstore as ns
>>> ns.to_dtype("struct { a u16, b i64, c f32 }").itemsize
14
>>> ns.to_dtype("union { a u16, b i64, c f32 }").itemsize
8
>>> ns.to_dtype("[10][20] u32").itemsize
800
>>> ns.to_dtype("[100] struct { x f32, y f32, z f32 }").itemsize
1200
>>> ns.to_dtype("struct { id u64, samples [8] cf64 }").itemsize
72
>>> ns.to_dtype("[12][256][256] struct { r u8, g u8, b u8 }").itemsize
2359296
>>> ns.to_dtype("struct { tag u8, payload union { a f64, b [2] u32 } }").itemsize
9