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use math;
use types;
// premature optimization ftw!
export def DIRECT: u8 = 0;
export def CONSTANT: u8 = 1;
export def INLINE_MAX: u8 = ((size(*opaque) * 2 - 1) / 2): u8;
export type Array = union {
// (2024 note): this used to use duplicate struct member names, which i guess
// was a compiler bug and doesn't work anymore.
struct { // direct
palette_size: u8, // == DIRECT
data_direct: *[*]u16,
},
struct { // constant
palette_size_const: u8, // == CONSTANT
data_constant: u16,
},
struct { // indirect inline
palette_size_indirect_inline: u8, // <= INLINE_MAX, != DIRECT, != CONSTANT
palette_inline: [INLINE_MAX]u16,
data_indirect: *[*]u8,
},
struct { // indirect ptr
palette_size_indirect_ptr: u8, // > INLINE_MAX
palette_ptr: *[*]u16,
// data_indirect: *[*]u8,
// (though it would result in an incorrect offset... yeah,
// i don't know what i was thinking here at all.)
},
};
export fn new(palette_size: u8, arraylen: size) Array = {
let array = Array {
palette_size = palette_size,
};
if (palette_size == DIRECT) {
array.data_direct =
alloc([]: [0]u16, arraylen): *[*]u16;
} else if (palette_size != CONSTANT) {
array.data_indirect = alloc([]: [0]u8,
indirect_size(palette_size, arraylen)): *[*]u8;
if (palette_size > INLINE_MAX) {
array.palette_ptr =
alloc([]: [0]u16, palette_size): *[*]u16;
};
};
return array;
};
export fn clear(array: *Array, fill_value: u16) void = {
if (array.palette_size == DIRECT) {
free(array.data_direct);
} else if (array.palette_size != CONSTANT) {
free(array.data_indirect);
if (array.palette_size > INLINE_MAX)
free(array.palette_ptr);
};
array.palette_size = CONSTANT;
array.data_constant = fill_value;
};
// XXX: should be @inline
export fn get(array: *Array, i: size) u16 = {
if (array.palette_size == DIRECT) {
return array.data_direct[i];
} else if (array.palette_size == CONSTANT) {
return 0;
} else {
const log2nbits = palette_log2nbits(array.palette_size);
const nbits = 1 << log2nbits;
const valuemask = (1 << nbits) - 1;
const log2nperbyte = 3 - log2nbits;
const nperbyte = 1 << log2nperbyte;
const indexlow = nperbyte - 1;
const byte = array.data_indirect[i >> log2nperbyte];
const shift = (i: u8 & indexlow) << log2nbits;
return (byte >> shift) & valuemask;
};
};
// XXX: should be @inline
export fn set(array: *Array, i: size, ref: u16) void = {
if (array.palette_size == DIRECT) {
array.data_direct[i] = ref;
} else if (array.palette_size == CONSTANT) {
assert(ref == 0);
} else {
const log2nbits = palette_log2nbits(array.palette_size);
const nbits = 1 << log2nbits;
const valuemask = (1 << nbits) - 1;
const log2nperbyte = 3 - log2nbits;
const nperbyte = 1 << log2nperbyte;
const indexlow = nperbyte - 1;
const byte = &array.data_indirect[i >> log2nperbyte];
const shift = (i: u8 & indexlow) << log2nbits;
*byte = *byte & ~(valuemask << shift) | ref: u8 << shift;
};
};
// XXX: should be @inline
export fn get_palette(array: *Array) []u16 = {
if (array.palette_size == DIRECT) {
abort();
} else if (array.palette_size == CONSTANT) {
return &array.data_constant: *[1]u16;
} else if (array.palette_size <= INLINE_MAX) {
return array.palette_inline[..array.palette_size];
} else {
return array.palette_ptr[..array.palette_size];
};
};
// XXX: should be @inline
export fn lookup(array: *Array, ref: u16) u16 = {
if (array.palette_size == DIRECT) {
return ref;
};
return get_palette(array)[ref];
};
// XXX: should be @inline
export fn indirect_size(palette_size: u8, arraylen: size) size =
arraylen << palette_log2nbits(palette_size) >> 3;
// XXX: should be @inline
export fn palette_log2nbits(palette_size: u8) u8 = {
assert(palette_size != DIRECT);
const nbits = math::bit_size_u8(palette_size - 1);
return math::bit_size_u8(nbits - 1);
};
export fn grow_palette(array: *Array, arraylen: size, newsize: u8) void = {
if (array.palette_size == newsize) return;
assert(
(array.palette_size - 1) < (newsize - 1),
"new size must be >= old size"
);
let newarray = *array;
newarray.palette_size = newsize;
defer *array = newarray;
// By this point we know that the palette has grown in size, so it
// always needs to be reallocated unless the new size is DIRECT,
// in which case there will be no palette.
const palette = get_palette(array);
if (newsize == DIRECT) {
void;
} else if (newsize <= INLINE_MAX) {
newarray.palette_inline[..len(palette)] = palette;
} else {
let newpalette = alloc(palette, newsize);
newarray.palette_ptr = newpalette: *[*]u16;
};
defer if (array.palette_size > INLINE_MAX) {
free(array.palette_ptr);
};
if (array.palette_size == CONSTANT) {
if (newsize == DIRECT) {
newarray.data_direct = alloc([array.data_constant...],
arraylen): *[*]u16;
} else {
newarray.data_indirect = alloc([0...],
indirect_size(newsize, arraylen)): *[*]u8;
};
return;
};
if (newsize == DIRECT) {
newarray.data_direct = alloc([]: [0]u16, arraylen): *[*]u16;
for (let i = 0z; i < arraylen; i += 1) {
newarray.data_direct[i] = palette[get(array, i)];
};
free(array.data_indirect);
return;
};
// We need to reallocate the data array if the number of bits per item
// increased.
const log2nbits = palette_log2nbits(array.palette_size);
const log2newnbits = palette_log2nbits(newsize);
if (log2nbits != log2newnbits) {
newarray.data_indirect = alloc([]: [0]u8,
indirect_size(newsize, arraylen)): *[*]u8;
for (let i = 0z; i < arraylen; i += 1) {
set(&newarray, i, get(array, i));
};
free(array.data_indirect);
};
};
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