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const std = @import("std");
/// default EntityTraitsDefinition with reasonable sizes suitable for most situations
pub const EntityTraits = EntityTraitsType(.medium);
pub const EntityTraitsSize = enum { small, medium, large };
pub fn EntityTraitsType(comptime size: EntityTraitsSize) type {
return switch (size) {
.small => EntityTraitsDefinition(u16, u12, u4),
.medium => EntityTraitsDefinition(u32, u20, u12),
.large => EntityTraitsDefinition(u64, u32, u32),
};
}
fn EntityTraitsDefinition(comptime EntityType: type, comptime IndexType: type, comptime VersionType: type) type {
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std.debug.assert(@typeInfo(EntityType) == .Int and std.meta.Int(.unsigned, @bitSizeOf(EntityType)) == EntityType);
std.debug.assert(@typeInfo(IndexType) == .Int and std.meta.Int(.unsigned, @bitSizeOf(IndexType)) == IndexType);
std.debug.assert(@typeInfo(VersionType) == .Int and std.meta.Int(.unsigned, @bitSizeOf(VersionType)) == VersionType);
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if (@bitSizeOf(IndexType) + @bitSizeOf(VersionType) != @bitSizeOf(EntityType))
@compileError("IndexType and VersionType must sum to EntityType's bit count");
return struct {
entity_type: type = EntityType,
index_type: type = IndexType,
version_type: type = VersionType,
/// Mask to use to get the entity index number out of an identifier
entity_mask: EntityType = std.math.maxInt(IndexType),
/// Mask to use to get the version out of an identifier
version_mask: EntityType = std.math.maxInt(VersionType),
pub fn init() @This() {
return @This(){};
}
};
}
test "entity traits" {
const sm = EntityTraitsType(.small).init();
const m = EntityTraitsType(.medium).init();
const l = EntityTraitsType(.large).init();
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try std.testing.expectEqual(sm.entity_mask, std.math.maxInt(sm.index_type));
try std.testing.expectEqual(m.entity_mask, std.math.maxInt(m.index_type));
try std.testing.expectEqual(l.entity_mask, std.math.maxInt(l.index_type));
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}