--- /dev/null
+Name
+
+ MESA_shader_integer_functions
+
+Name Strings
+
+ GL_MESA_shader_integer_functions
+
+Contact
+
+ Ian Romanick <ian.d.romanick@intel.com>
+
+Contributors
+
+ All the contributors of GL_ARB_gpu_shader5
+
+Status
+
+ Supported by all GLSL 1.30 capable drivers in Mesa 12.1 and later
+
+Version
+
+ Version 2, July 7, 2016
+
+Number
+
+ TBD
+
+Dependencies
+
+ This extension is written against the OpenGL 3.2 (Compatibility Profile)
+ Specification.
+
+ This extension is written against Version 1.50 (Revision 09) of the OpenGL
+ Shading Language Specification.
+
+ GLSL 1.30 is required.
+
+ This extension interacts with ARB_gpu_shader5.
+
+ This extension interacts with ARB_gpu_shader_fp64.
+
+ This extension interacts with NV_gpu_shader5.
+
+Overview
+
+ GL_ARB_gpu_shader5 extends GLSL in a number of useful ways. Much of this
+ added functionality requires significant hardware support. There are many
+ aspects, however, that can be easily implmented on any GPU with "real"
+ integer support (as opposed to simulating integers using floating point
+ calculations).
+
+ This extension provides a set of new features to the OpenGL Shading
+ Language to support capabilities of these GPUs, extending the capabilities
+ of version 1.30 of the OpenGL Shading Language. Shaders
+ using the new functionality provided by this extension should enable this
+ functionality via the construct
+
+ #extension GL_MESA_shader_integer_functions : require (or enable)
+
+ This extension provides a variety of new features for all shader types,
+ including:
+
+ * support for implicitly converting signed integer types to unsigned
+ types, as well as more general implicit conversion and function
+ overloading infrastructure to support new data types introduced by
+ other extensions;
+
+ * new built-in functions supporting:
+
+ * splitting a floating-point number into a significand and exponent
+ (frexp), or building a floating-point number from a significand and
+ exponent (ldexp);
+
+ * integer bitfield manipulation, including functions to find the
+ position of the most or least significant set bit, count the number
+ of one bits, and bitfield insertion, extraction, and reversal;
+
+ * extended integer precision math, including add with carry, subtract
+ with borrow, and extenended multiplication;
+
+ The resulting extension is a strict subset of GL_ARB_gpu_shader5.
+
+IP Status
+
+ No known IP claims.
+
+New Procedures and Functions
+
+ None
+
+New Tokens
+
+ None
+
+Additions to Chapter 2 of the OpenGL 3.2 (Compatibility Profile) Specification
+(OpenGL Operation)
+
+ None.
+
+Additions to Chapter 3 of the OpenGL 3.2 (Compatibility Profile) Specification
+(Rasterization)
+
+ None.
+
+Additions to Chapter 4 of the OpenGL 3.2 (Compatibility Profile) Specification
+(Per-Fragment Operations and the Frame Buffer)
+
+ None.
+
+Additions to Chapter 5 of the OpenGL 3.2 (Compatibility Profile) Specification
+(Special Functions)
+
+ None.
+
+Additions to Chapter 6 of the OpenGL 3.2 (Compatibility Profile) Specification
+(State and State Requests)
+
+ None.
+
+Additions to Appendix A of the OpenGL 3.2 (Compatibility Profile)
+Specification (Invariance)
+
+ None.
+
+Additions to the AGL/GLX/WGL Specifications
+
+ None.
+
+Modifications to The OpenGL Shading Language Specification, Version 1.50
+(Revision 09)
+
+ Including the following line in a shader can be used to control the
+ language features described in this extension:
+
+ #extension GL_MESA_shader_integer_functions : <behavior>
+
+ where <behavior> is as specified in section 3.3.
+
+ New preprocessor #defines are added to the OpenGL Shading Language:
+
+ #define GL_MESA_shader_integer_functions 1
+
+
+ Modify Section 4.1.10, Implicit Conversions, p. 27
+
+ (modify table of implicit conversions)
+
+ Can be implicitly
+ Type of expression converted to
+ --------------------- -----------------
+ int uint, float
+ ivec2 uvec2, vec2
+ ivec3 uvec3, vec3
+ ivec4 uvec4, vec4
+
+ uint float
+ uvec2 vec2
+ uvec3 vec3
+ uvec4 vec4
+
+ (modify second paragraph of the section) No implicit conversions are
+ provided to convert from unsigned to signed integer types or from
+ floating-point to integer types. There are no implicit array or structure
+ conversions.
+
+ (insert before the final paragraph of the section) When performing
+ implicit conversion for binary operators, there may be multiple data types
+ to which the two operands can be converted. For example, when adding an
+ int value to a uint value, both values can be implicitly converted to uint
+ and float. In such cases, a floating-point type is chosen if either
+ operand has a floating-point type. Otherwise, an unsigned integer type is
+ chosen if either operand has an unsigned integer type. Otherwise, a
+ signed integer type is chosen.
+
+
+ Modify Section 5.9, Expressions, p. 57
+
+ (modify bulleted list as follows, adding support for implicit conversion
+ between signed and unsigned types)
+
+ Expressions in the shading language are built from the following:
+
+ * Constants of type bool, int, int64_t, uint, uint64_t, float, all vector
+ types, and all matrix types.
+
+ ...
+
+ * The operator modulus (%) operates on signed or unsigned integer scalars
+ or vectors. If the fundamental types of the operands do not match, the
+ conversions from Section 4.1.10 "Implicit Conversions" are applied to
+ produce matching types. ...
+
+
+ Modify Section 6.1, Function Definitions, p. 63
+
+ (modify description of overloading, beginning at the top of p. 64)
+
+ Function names can be overloaded. The same function name can be used for
+ multiple functions, as long as the parameter types differ. If a function
+ name is declared twice with the same parameter types, then the return
+ types and all qualifiers must also match, and it is the same function
+ being declared. For example,
+
+ vec4 f(in vec4 x, out vec4 y); // (A)
+ vec4 f(in vec4 x, out uvec4 y); // (B) okay, different argument type
+ vec4 f(in ivec4 x, out uvec4 y); // (C) okay, different argument type
+
+ int f(in vec4 x, out ivec4 y); // error, only return type differs
+ vec4 f(in vec4 x, in vec4 y); // error, only qualifier differs
+ vec4 f(const in vec4 x, out vec4 y); // error, only qualifier differs
+
+ When function calls are resolved, an exact type match for all the
+ arguments is sought. If an exact match is found, all other functions are
+ ignored, and the exact match is used. If no exact match is found, then
+ the implicit conversions in Section 4.1.10 (Implicit Conversions) will be
+ applied to find a match. Mismatched types on input parameters (in or
+ inout or default) must have a conversion from the calling argument type
+ to the formal parameter type. Mismatched types on output parameters (out
+ or inout) must have a conversion from the formal parameter type to the
+ calling argument type.
+
+ If implicit conversions can be used to find more than one matching
+ function, a single best-matching function is sought. To determine a best
+ match, the conversions between calling argument and formal parameter
+ types are compared for each function argument and pair of matching
+ functions. After these comparisons are performed, each pair of matching
+ functions are compared. A function definition A is considered a better
+ match than function definition B if:
+
+ * for at least one function argument, the conversion for that argument
+ in A is better than the corresponding conversion in B; and
+
+ * there is no function argument for which the conversion in B is better
+ than the corresponding conversion in A.
+
+ If a single function definition is considered a better match than every
+ other matching function definition, it will be used. Otherwise, a
+ semantic error occurs and the shader will fail to compile.
+
+ To determine whether the conversion for a single argument in one match is
+ better than that for another match, the following rules are applied, in
+ order:
+
+ 1. An exact match is better than a match involving any implicit
+ conversion.
+
+ 2. A match involving an implicit conversion from float to double is
+ better than a match involving any other implicit conversion.
+
+ 3. A match involving an implicit conversion from either int or uint to
+ float is better than a match involving an implicit conversion from
+ either int or uint to double.
+
+ If none of the rules above apply to a particular pair of conversions,
+ neither conversion is considered better than the other.
+
+ For the function prototypes (A), (B), and (C) above, the following
+ examples show how the rules apply to different sets of calling argument
+ types:
+
+ f(vec4, vec4); // exact match of vec4 f(in vec4 x, out vec4 y)
+ f(vec4, uvec4); // exact match of vec4 f(in vec4 x, out ivec4 y)
+ f(vec4, ivec4); // matched to vec4 f(in vec4 x, out vec4 y)
+ // (C) not relevant, can't convert vec4 to
+ // ivec4. (A) better than (B) for 2nd
+ // argument (rule 2), same on first argument.
+ f(ivec4, vec4); // NOT matched. All three match by implicit
+ // conversion. (C) is better than (A) and (B)
+ // on the first argument. (A) is better than
+ // (B) and (C).
+
+
+ Modify Section 8.3, Common Functions, p. 84
+
+ (add support for single-precision frexp and ldexp functions)
+
+ Syntax:
+
+ genType frexp(genType x, out genIType exp);
+ genType ldexp(genType x, in genIType exp);
+
+ The function frexp() splits each single-precision floating-point number in
+ <x> into a binary significand, a floating-point number in the range [0.5,
+ 1.0), and an integral exponent of two, such that:
+
+ x = significand * 2 ^ exponent
+
+ The significand is returned by the function; the exponent is returned in
+ the parameter <exp>. For a floating-point value of zero, the significant
+ and exponent are both zero. For a floating-point value that is an
+ infinity or is not a number, the results of frexp() are undefined.
+
+ If the input <x> is a vector, this operation is performed in a
+ component-wise manner; the value returned by the function and the value
+ written to <exp> are vectors with the same number of components as <x>.
+
+ The function ldexp() builds a single-precision floating-point number from
+ each significand component in <x> and the corresponding integral exponent
+ of two in <exp>, returning:
+
+ significand * 2 ^ exponent
+
+ If this product is too large to be represented as a single-precision
+ floating-point value, the result is considered undefined.
+
+ If the input <x> is a vector, this operation is performed in a
+ component-wise manner; the value passed in <exp> and returned by the
+ function are vectors with the same number of components as <x>.
+
+
+ (add support for new integer built-in functions)
+
+ Syntax:
+
+ genIType bitfieldExtract(genIType value, int offset, int bits);
+ genUType bitfieldExtract(genUType value, int offset, int bits);
+
+ genIType bitfieldInsert(genIType base, genIType insert, int offset,
+ int bits);
+ genUType bitfieldInsert(genUType base, genUType insert, int offset,
+ int bits);
+
+ genIType bitfieldReverse(genIType value);
+ genUType bitfieldReverse(genUType value);
+
+ genIType bitCount(genIType value);
+ genIType bitCount(genUType value);
+
+ genIType findLSB(genIType value);
+ genIType findLSB(genUType value);
+
+ genIType findMSB(genIType value);
+ genIType findMSB(genUType value);
+
+ The function bitfieldExtract() extracts bits <offset> through
+ <offset>+<bits>-1 from each component in <value>, returning them in the
+ least significant bits of corresponding component of the result. For
+ unsigned data types, the most significant bits of the result will be set
+ to zero. For signed data types, the most significant bits will be set to
+ the value of bit <offset>+<base>-1. If <bits> is zero, the result will be
+ zero. The result will be undefined if <offset> or <bits> is negative, or
+ if the sum of <offset> and <bits> is greater than the number of bits used
+ to store the operand. Note that for vector versions of bitfieldExtract(),
+ a single pair of <offset> and <bits> values is shared for all components.
+
+ The function bitfieldInsert() inserts the <bits> least significant bits of
+ each component of <insert> into the corresponding component of <base>.
+ The result will have bits numbered <offset> through <offset>+<bits>-1
+ taken from bits 0 through <bits>-1 of <insert>, and all other bits taken
+ directly from the corresponding bits of <base>. If <bits> is zero, the
+ result will simply be <base>. The result will be undefined if <offset> or
+ <bits> is negative, or if the sum of <offset> and <bits> is greater than
+ the number of bits used to store the operand. Note that for vector
+ versions of bitfieldInsert(), a single pair of <offset> and <bits> values
+ is shared for all components.
+
+ The function bitfieldReverse() reverses the bits of <value>. The bit
+ numbered <n> of the result will be taken from bit (<bits>-1)-<n> of
+ <value>, where <bits> is the total number of bits used to represent
+ <value>.
+
+ The function bitCount() returns the number of one bits in the binary
+ representation of <value>.
+
+ The function findLSB() returns the bit number of the least significant one
+ bit in the binary representation of <value>. If <value> is zero, -1 will
+ be returned.
+
+ The function findMSB() returns the bit number of the most significant bit
+ in the binary representation of <value>. For positive integers, the
+ result will be the bit number of the most significant one bit. For
+ negative integers, the result will be the bit number of the most
+ significant zero bit. For a <value> of zero or negative one, -1 will be
+ returned.
+
+
+ (support for unsigned integer add/subtract with carry-out)
+
+ Syntax:
+
+ genUType uaddCarry(genUType x, genUType y, out genUType carry);
+ genUType usubBorrow(genUType x, genUType y, out genUType borrow);
+
+ The function uaddCarry() adds 32-bit unsigned integers or vectors <x> and
+ <y>, returning the sum modulo 2^32. The value <carry> is set to zero if
+ the sum was less than 2^32, or one otherwise.
+
+ The function usubBorrow() subtracts the 32-bit unsigned integer or vector
+ <y> from <x>, returning the difference if non-negative or 2^32 plus the
+ difference, otherwise. The value <borrow> is set to zero if x >= y, or
+ one otherwise.
+
+
+ (support for signed and unsigned multiplies, with 32-bit inputs and a
+ 64-bit result spanning two 32-bit outputs)
+
+ Syntax:
+
+ void umulExtended(genUType x, genUType y, out genUType msb,
+ out genUType lsb);
+ void imulExtended(genIType x, genIType y, out genIType msb,
+ out genIType lsb);
+
+ The functions umulExtended() and imulExtended() multiply 32-bit unsigned
+ or signed integers or vectors <x> and <y>, producing a 64-bit result. The
+ 32 least significant bits are returned in <lsb>; the 32 most significant
+ bits are returned in <msb>.
+
+
+GLX Protocol
+
+ None.
+
+Dependencies on ARB_gpu_shader_fp64
+
+ This extension, ARB_gpu_shader_fp64, and NV_gpu_shader5 all modify the set
+ of implicit conversions supported in the OpenGL Shading Language. If more
+ than one of these extensions is supported, an expression of one type may
+ be converted to another type if that conversion is allowed by any of these
+ specifications.
+
+ If ARB_gpu_shader_fp64 or a similar extension introducing new data types
+ is not supported, the function overloading rule in the GLSL specification
+ preferring promotion an input parameters to smaller type to a larger type
+ is never applicable, as all data types are of the same size. That rule
+ and the example referring to "double" should be removed.
+
+
+Dependencies on NV_gpu_shader5
+
+ This extension, ARB_gpu_shader_fp64, and NV_gpu_shader5 all modify the set
+ of implicit conversions supported in the OpenGL Shading Language. If more
+ than one of these extensions is supported, an expression of one type may
+ be converted to another type if that conversion is allowed by any of these
+ specifications.
+
+ If NV_gpu_shader5 is supported, integer data types are supported with four
+ different precisions (8-, 16, 32-, and 64-bit) and floating-point data
+ types are supported with three different precisions (16-, 32-, and
+ 64-bit). The extension adds the following rule for output parameters,
+ which is similar to the one present in this extension for input
+ parameters:
+
+ 5. If the formal parameters in both matches are output parameters, a
+ conversion from a type with a larger number of bits per component is
+ better than a conversion from a type with a smaller number of bits
+ per component. For example, a conversion from an "int16_t" formal
+ parameter type to "int" is better than one from an "int8_t" formal
+ parameter type to "int".
+
+ Such a rule is not provided in this extension because there is no
+ combination of types in this extension and ARB_gpu_shader_fp64 where this
+ rule has any effect.
+
+
+Errors
+
+ None
+
+
+New State
+
+ None
+
+New Implementation Dependent State
+
+ None
+
+Issues
+
+ (1) What should this extension be called?
+
+ UNRESOLVED. This extension borrows from GL_ARB_gpu_shader5, so creating
+ some sort of a play on that name would be viable. However, nothing in
+ this extension should require SM5 hardware, so such a name would be a
+ little misleading and weird.
+
+ Since the primary purpose is to add integer related functions from
+ GL_ARB_gpu_shader5, call this extension GL_MESA_shader_integer_functions
+ for now.
+
+ (2) Why is some of the formatting in this extension weird?
+
+ RESOLVED: This extension is formatted to minimize the differences (as
+ reported by 'diff --side-by-side -W180') with the GL_ARB_gpu_shader5
+ specification.
+
+ (3) Should ldexp and frexp be included?
+
+ RESOLVED: Yes. Few GPUs have native instructions to implement these
+ functions. These are generally implemented using existing GLSL built-in
+ functions and the other functions provided by this extension.
+
+ (4) Should umulExtended and imulExtended be included?
+
+ RESOLVED: Yes. These functions should be implementable on any GPU that
+ can support the rest of this extension, but the implementation may be
+ complex. The implementation on a GPU that only supports 32bit x 32bit =
+ 32bit multiplication would be quite expensive. However, many GPUs
+ (including OpenGL 4.0 GPUs that already support this function) have a
+ 32bit x 16bit = 48bit multiplier. The implementation there is only
+ trivially more expensive than regular 32bit multiplication.
+
+ (5) Should the pack and unpack functions be included?
+
+ RESOLVED: No. These functions are already available via
+ GL_ARB_shading_language_packing.
+
+ (6) Should the "BitsTo" functions be included?
+
+ RESOLVED: No. These functions are already available via
+ GL_ARB_shader_bit_encoding.
+
+Revision History
+
+ Rev. Date Author Changes
+ ---- ----------- -------- -----------------------------------------
+ 2 7-Jul-2016 idr Fix typo in #extension line
+ 1 20-Jun-2016 idr Initial version based on GL_ARB_gpu_shader5.
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