STC cspan: Multi-dimensional Array View
The cspan types are templated non-owning single and multi-dimensional views of an array. It supports both row-major and column-major layout efficiently, in a addition to slicing capabilities similar to python's numpy arrays. Note that each dimension is currently limited to int32_t sizes and 8 dimensions (can be extended).
See also C++ std::span / std::mdspan for similar functionality.
cspan types are defined by the using_cspan() macro after the header is included. This is different from other containers where template parameters are defined prior to including each container. This works well mainly because cspan is non-owning.
#include "stc/cspan.h"
using_cspan(SpanType, ValueType); // define a 1-d SpanType with ValueType elements.
using_cspan(SpanTypeN, ValueType, RANK); // define multi-dimensional span with RANK.
// RANK is the literal number of dimensions
// Shorthands:
using_cspan2(S, ValueType); // define span types S, S2 with ranks 1, 2.
using_cspan3(S, ValueType); // define span types S, S2, S3 with ranks 1, 2, 3.
using_cspan4(S, ValueType); // define span types S, S2, S3, S4 with ranks 1, 2, 3, 4.All functions are type-safe. NOTE: the span argument itself is generally not side-effect safe -
it may be expanded multiple times. However, all index arguments are safe, e.g.
cspan_at(&ms3, i++, j++, k++) is safe, but cspan_at(&spans[n++], i, j) is an error! If the number
of arguments does not match the span rank, a compile error is issued. Runtime bounds checks are enabled
by default (define STC_NDEBUG or NDEBUG to disable).
SpanType cspan_init(<TYPE> SpanType, {v1, v2, ...}); // make a 1-d cspan from value list
SpanType cspan_from_n(ValueType* ptr, intptr_t n); // make a 1-d cspan from a pointer and length
SpanType cspan_from_array(ValueType array[]); // make a 1-d cspan from a C array
SpanType cspan_from(STCContainer* cnt); // make a 1-d cspan from a vec or stack
int cspan_rank(const SpanTypeN* self); // num dimensions; compile-time constant
intptr_t cspan_size(const SpanTypeN* self); // return number of elements
intptr_t cspan_index(const SpanTypeN* self, intptr_t i, j..); // offset index at i, j,...
ValueType* cspan_at(const SpanTypeN* self, intptr_t i, j..); // num args is compile-time checked
ValueType* cspan_front(const SpanTypeN* self);
ValueType* cspan_back(const SpanTypeN* self);
// print numpy style output.
// span : any dimension. Note that span is passed by value.
// fmt : printf format specifier.
// fp : optional output file pointer, default stdout.
// brackets : optional brackets and comma. Example "{},". Default "[]".
// itemfn : optional macro function
// Example: #define complexnum(e) e.real, e.imag
// Default: itemfn(e) e
// Note that fmt must match the arguments passed via itemfn().
// Usage ex: cspan_print(Span2, ((Span2)cspan_transposed2(&sp2)), "%.3f");
// cspan_print(Span2, cspan_slice(Span2, &sp3, {c_ALL}, {3}, {c_ALL}), "%.3f");
void cspan_print(<TYPE> SpanTypeN, SpanTypeN span, const char* fmt,
FILE* fp = stdout, const char* brackets = "[]", itemfn = c_EXPAND);
SpanTypeN_iter SpanType_begin(const SpanTypeN* self);
SpanTypeN_iter SpanType_end(const SpanTypeN* self);
void SpanType_next(SpanTypeN_iter* it);
// construct a multi-dim span
SpanTypeN cspan_md(ValueType* data, intptr_t d1, d2...); // row-major layout
SpanTypeN cspan_md_layout(cspan_layout layout, ValueType* data, intptr_t d1, d2...);
// transpose an md span. Inverses layout and axes only.
void cspan_swap_axes(SpanTypeN* self, int ax1, int ax2);
void cspan_transpose(SpanTypeN* self);
SpanType2 cspan_transposed2(const SpanType2* self); // constructor
cspan_layout cspan_get_layout(const SpanTypeN* self);
bool cspan_is_rowmajor(const SpanTypeN* self);
bool cspan_is_colmajor(const SpanTypeN* self);
// construct a 1d subspan. Like cspan_slice(Span, &ms, {offset, offset+count});
SpanType1 cspan_subspan(const SpanType1* self, intptr_t offset, intptr_t count);
// construct submd span of lower rank. Like e.g. cspan_slice(Span2, &ms4, {i}, {j}, {c_ALL}, {c_ALL});
OutSpan1 cspan_submd2(const SpanType2* self, intptr_t i); // construct a 1d subspan from a 2d span.
OutSpanM cspan_submd3(const SpanType3* self, intptr_t i,...); // construct a 2d or 1d subspan from a 3d span.
OutSpanM cspan_submd4(const SpanType4* self, intptr_t i,...); // construct a 3d, 2d or 1d subspan from a 4d span.
// multi-dim span slicing function.
// {i}: select i'th column. reduce output rank.
// {i,j}: from i to j-1.
// {i,j,s}: every s column only (default s=1)
// {i,c_END}: from i to last.
// {c_ALL}: full extent, like {0,c_END}.
OutSpanM cspan_slice(<TYPE> OutSpanM, const SpanTypeN* self, {x0,x1,xs}, {y0,y1,ys}.., {N0,N1,Ns});| Type name | Type definition / usage | Used to represent... |
|---|---|---|
| STC_CSPAN_INDEX_TYPE | Defines cextent_t, default int32_t |
Index type |
| SpanTypeN_value | ValueType |
The ValueType |
| SpanTypeN | struct { ValueType *data; cextent_t shape[N]; .. } |
SpanType with rank N |
cspan_tupleN |
struct { cextent_t d[N]; } |
Strides for each rank |
cspan_layout |
enum { c_ROWMAJOR, c_COLMAJOR } |
Multi-dim layout |
c_ALL |
cspan_slice(&md, {1,3}, {c_ALL}) |
Full extent |
c_END |
cspan_slice(&md, {1,c_END}, {2,c_END}) |
End of extent |
[ Run this code ]
#include <stdio.h>
#define i_key int
#include "stc/vec.h"
#define i_key int
#include "stc/stack.h"
#include "stc/cspan.h"
using_cspan(intspan, int);
void printMe(intspan container) {
printf("%d:", (int)cspan_size(&container));
c_foreach (e, intspan, container)
printf(" %d", *e.ref);
puts("");
}
int main(void)
{
printMe( c_init(intspan, {1, 2, 3, 4}) );
int arr[] = {1, 2, 3, 4, 5};
printMe( (intspan)cspan_from_array(arr) );
vec_int vec = c_init(vec_int, {1, 2, 3, 4, 5, 6});
printMe( (intspan)cspan_from(&vec) );
stack_int stk = c_init(stack_int, {1, 2, 3, 4, 5, 6, 7});
printMe( (intspan)cspan_from(&stk) );
intspan spn = c_init(intspan, {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12});
printMe( (intspan)cspan_subspan(&spn, 2, 8) );
// cleanup
vec_int_drop(&vec);
stack_int_drop(&stk);
}Multi-dimension slicing (first in python):
import numpy as np
def print_myspan2(s2):
for i in range(s2.shape[0]):
for j in range(s2.shape[1]):
print(" {}".format(s2[i, j]), end='')
print('')
print('')
if __name__ == '__main__':
ms3 = np.array((1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24), int)
ms3 = np.reshape(ms3, (2, 3, 4), order='C')
ss3 = ms3[:, 0:3, 2:]
a = ss3[1]
b = np.transpose(a)
print_myspan2(ms3[1])
print_myspan2(a)
print_myspan2(b)
for i in a.flat: print(" {}".format(i), end='')
print('')
for i in b.flat: print(" {}".format(i), end='')
'''
13 14 15 16
17 18 19 20
21 22 23 24
15 16
19 20
23 24
15 19 23
16 20 24
15 16 19 20 23 24
15 19 23 16 20 24
'''... in C with STC cspan:
[ Run this code ]
#include <stdio.h>
#include "stc/cspan.h"
using_cspan3(myspan, int); // define myspan, myspan2, myspan3.
void print_myspan2(myspan2 ms) {
for (int i=0; i < ms.shape[0]; ++i) {
for (int j=0; j < ms.shape[1]; ++j)
printf(" %2d", *cspan_at(&ms, i, j));
puts("");
}
puts("");
}
int main(void) {
int arr[] = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24};
myspan3 ms3 = cspan_md(arr, 2, 3, 4); // row-major layout
myspan3 ss3 = cspan_slice(myspan3, &ms3, {c_ALL}, {0,3}, {2,c_END});
myspan2 a = cspan_submd3(&ss3, 1);
myspan2 b = cspan_transposed2(&a);
cspan_print(myspan3, ss3); // C11. Add "%d" argument for C99 comp.
puts("");
print_myspan2((myspan2)cspan_submd3(&ms3, 1));
print_myspan2(a);
print_myspan2(b);
c_foreach (i, myspan2, a) printf(" %d", *i.ref);
puts("");
c_foreach (i, myspan2, b) printf(" %d", *i.ref);
puts("");
}Slicing cspan without and with reducing the rank:
[ Run this code ]
#include <stdio.h>
#include "stc/cspan.h"
using_cspan3(Span, int); // Shorthand to define Span, Span2, and Span3
int main(void)
{
Span span = c_init(Span, {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24});
Span3 span3 = cspan_md(span.data, 2, 4, 3);
// numpy style printout
puts("span3:");
cspan_print(Span3, span3, "%d");
puts("Slice without reducing rank:");
Span3 ss3 = cspan_slice(Span3, &span3, {c_ALL}, {3,4}, {c_ALL});
cspan_print(Span3, ss3);
puts("Slice with reducing rank:");
Span2 ss2 = cspan_slice(Span2, &span3, {c_ALL}, {3}, {c_ALL});
cspan_print(Span2, ss2);
puts("Swapped:");
Span3 swapped = span3;
cspan_swap_axes(&swapped, 0, 1);
cspan_swap_axes(&swapped, 1, 2);
cspan_print(Span3, swapped);
}