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Diffstat (limited to 'llvm/docs')
| -rw-r--r-- | llvm/docs/LangRef.rst | 145 |
1 files changed, 141 insertions, 4 deletions
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index 97e454e5e53..a64974c2d90 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -13675,16 +13675,17 @@ Fixed Point Arithmetic Intrinsics A fixed point number represents a real data type for a number that has a fixed number of digits after a radix point (equivalent to the decimal point '.'). -The number of digits after the radix point is referred as the ``scale``. These +The number of digits after the radix point is referred as the `scale`. These are useful for representing fractional values to a specific precision. The following intrinsics perform fixed point arithmetic operations on 2 operands of the same scale, specified as the third argument. -The `llvm.*mul.fix` family of intrinsic functions represents a multiplication +The ``llvm.*mul.fix`` family of intrinsic functions represents a multiplication of fixed point numbers through scaled integers. Therefore, fixed point -multplication can be represented as +multiplication can be represented as + +.. code-block:: llvm -:: %result = call i4 @llvm.smul.fix.i4(i4 %a, i4 %b, i32 %scale) ; Expands to @@ -13695,6 +13696,22 @@ multplication can be represented as %r = ashr i8 %mul, i8 %scale2 ; this is for a target rounding down towards negative infinity %result = trunc i8 %r to i4 +The ``llvm.*div.fix`` family of intrinsic functions represents a division of +fixed point numbers through scaled integers. Fixed point division can be +represented as: + +.. code-block:: llvm + + %result call i4 @llvm.sdiv.fix.i4(i4 %a, i4 %b, i32 %scale) + + ; Expands to + %a2 = sext i4 %a to i8 + %b2 = sext i4 %b to i8 + %scale2 = trunc i32 %scale to i8 + %a3 = shl i8 %a2, %scale2 + %r = sdiv i8 %a3, %b2 ; this is for a target rounding towards zero + %result = trunc i8 %r to i4 + For each of these functions, if the result cannot be represented exactly with the provided scale, the result is rounded. Rounding is unspecified since preferred rounding may vary for different targets. Rounding is specified @@ -13963,6 +13980,126 @@ Examples %res = call i4 @llvm.umul.fix.sat.i4(i4 2, i4 4, i32 1) ; %res = 4 (1 x 2 = 2) +'``llvm.sdiv.fix.*``' Intrinsics +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Syntax +""""""" + +This is an overloaded intrinsic. You can use ``llvm.sdiv.fix`` +on any integer bit width or vectors of integers. + +:: + + declare i16 @llvm.sdiv.fix.i16(i16 %a, i16 %b, i32 %scale) + declare i32 @llvm.sdiv.fix.i32(i32 %a, i32 %b, i32 %scale) + declare i64 @llvm.sdiv.fix.i64(i64 %a, i64 %b, i32 %scale) + declare <4 x i32> @llvm.sdiv.fix.v4i32(<4 x i32> %a, <4 x i32> %b, i32 %scale) + +Overview +""""""""" + +The '``llvm.sdiv.fix``' family of intrinsic functions perform signed +fixed point division on 2 arguments of the same scale. + +Arguments +"""""""""" + +The arguments (%a and %b) and the result may be of integer types of any bit +width, but they must have the same bit width. The arguments may also work with +int vectors of the same length and int size. ``%a`` and ``%b`` are the two +values that will undergo signed fixed point division. The argument +``%scale`` represents the scale of both operands, and must be a constant +integer. + +Semantics: +"""""""""" + +This operation performs fixed point division on the 2 arguments of a +specified scale. The result will also be returned in the same scale specified +in the third argument. + +If the result value cannot be precisely represented in the given scale, the +value is rounded up or down to the closest representable value. The rounding +direction is unspecified. + +It is undefined behavior if the result value does not fit within the range of +the fixed point type, or if the second argument is zero. + + +Examples +""""""""" + +.. code-block:: llvm + + %res = call i4 @llvm.sdiv.fix.i4(i4 6, i4 2, i32 0) ; %res = 3 (6 / 2 = 3) + %res = call i4 @llvm.sdiv.fix.i4(i4 6, i4 4, i32 1) ; %res = 3 (3 / 2 = 1.5) + %res = call i4 @llvm.sdiv.fix.i4(i4 3, i4 -2, i32 1) ; %res = -3 (1.5 / -1 = -1.5) + + ; The result in the following could be rounded up to 1 or down to 0.5 + %res = call i4 @llvm.sdiv.fix.i4(i4 3, i4 4, i32 1) ; %res = 2 (or 1) (1.5 / 2 = 0.75) + + +'``llvm.udiv.fix.*``' Intrinsics +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Syntax +""""""" + +This is an overloaded intrinsic. You can use ``llvm.udiv.fix`` +on any integer bit width or vectors of integers. + +:: + + declare i16 @llvm.udiv.fix.i16(i16 %a, i16 %b, i32 %scale) + declare i32 @llvm.udiv.fix.i32(i32 %a, i32 %b, i32 %scale) + declare i64 @llvm.udiv.fix.i64(i64 %a, i64 %b, i32 %scale) + declare <4 x i32> @llvm.udiv.fix.v4i32(<4 x i32> %a, <4 x i32> %b, i32 %scale) + +Overview +""""""""" + +The '``llvm.udiv.fix``' family of intrinsic functions perform unsigned +fixed point division on 2 arguments of the same scale. + +Arguments +"""""""""" + +The arguments (%a and %b) and the result may be of integer types of any bit +width, but they must have the same bit width. The arguments may also work with +int vectors of the same length and int size. ``%a`` and ``%b`` are the two +values that will undergo unsigned fixed point division. The argument +``%scale`` represents the scale of both operands, and must be a constant +integer. + +Semantics: +"""""""""" + +This operation performs fixed point division on the 2 arguments of a +specified scale. The result will also be returned in the same scale specified +in the third argument. + +If the result value cannot be precisely represented in the given scale, the +value is rounded up or down to the closest representable value. The rounding +direction is unspecified. + +It is undefined behavior if the result value does not fit within the range of +the fixed point type, or if the second argument is zero. + + +Examples +""""""""" + +.. code-block:: llvm + + %res = call i4 @llvm.udiv.fix.i4(i4 6, i4 2, i32 0) ; %res = 3 (6 / 2 = 3) + %res = call i4 @llvm.udiv.fix.i4(i4 6, i4 4, i32 1) ; %res = 3 (3 / 2 = 1.5) + %res = call i4 @llvm.udiv.fix.i4(i4 1, i4 -8, i32 4) ; %res = 2 (0.0625 / 0.5 = 0.125) + + ; The result in the following could be rounded up to 1 or down to 0.5 + %res = call i4 @llvm.udiv.fix.i4(i4 3, i4 4, i32 1) ; %res = 2 (or 1) (1.5 / 2 = 0.75) + + Specialised Arithmetic Intrinsics --------------------------------- |
