COMPUTE
A significant number of COMPUTE, ADD, SUBTRACT, MULTIPLY, DIVIDE statements show improved performance in V6.
Under "Data types" in the following examples, italics are used to indicate the variant tested for performance, but all data types listed would demonstrate similar performance results.
Larger decimal multiply/divide
Statement: COMPUTE (* | /), MULTIPLY, DIVIDE
Data types: COMP-3, DISPLAY, NATIONAL
Options: OPT(1 | 2)
Conditions: When intermediate results exceed the limits for using the hardware packed decimal instructions. This occurs at around 15 digits depending on the particular operation.
V4 behavior: Call to runtime routine
V6 behavior: Inline after converting to DFP
1 z14v2 pic s9(14)v9(2)
1 z13v2 pic s9(13)v9(2)
Compute z14v2 = z14v2 / z13v2.Performance: V6 is 43% faster than V4
Zoned decimal (DISPLAY) arithmetic
Statement: COMPUTE (+ | - | * | /), ADD, SUBTRACT, MULTIPLY, DIVIDE
Data types: DISPLAY
Options: OPT(1 | 2), ARCH(10)
Conditions: In all cases
V4 behavior: Inline using packed decimal instructions
V6 behavior: Inline after converting to DFP
1 z12v2 pic s9(12)v9(2)
1 z11v2 pic s9(11)v9(2)
Compute z12v2 = z12v2 / z11v2Performance: V6 is 59% faster than V4
Divide by powers of ten (10,100,1000,..)
Statement: COMPUTE (/), DIVIDE
Data types: COMP-3, DISPLAY, NATIONAL
Options: Default
Conditions: Divisor is a power of 10 (e.g. 10,100,1000,…)
V4 behavior: Use packed decimal divide (DP) instruction
V6 behavior: Model as decimal right shift
1 p8v2a pic s9(8)v9(2) comp-3
1 p8v2b pic s9(8)v9(2) comp-3
Compute p8v2b = p8v2a / 100Performance: V6 is 45% faster than V4
Multiply by powers of ten (10,100,1000,..)
Statement: COMPUTE (/), MULTIPLY
Data types: COMP-3, DISPLAY, NATIONAL
Options: Default
Conditions: Multiply is a power of 10 (e.g. 10,100,1000,…)
V4 behavior: Use packed decimal multiply (MP) instruction
V6 behavior: Model as decimal left shift
1 z5v2 pic s9(5)v9(2)
1 z7v2 pic s9(7)v9(2)
Compute z7v2 = z5v2 * 100Performance: V6 is 73% faster than V4
Decimal exponentiation
Statement: COMPUTE (**)
Data types: COMP-3, DISPLAY, NATIONAL
Options: Default
Conditions: In all cases
V4 behavior: Call to runtime routine
V6 behavior: Call to a more efficient runtime routine
1 R PIC 9v9(8) value 0.05.
1 NF PIC 9(4) value 300.
1 EXP PIC 9(23)v9(8).
COMPUTE EXP = (1.0 + R) ** NF.Performance: V6 is 96% faster than V4
Decimal scaling and divide
Statement: COMPUTE (/), DIVIDE
Data types: COMP-3, DISPLAY, NATIONAL
Options: Default
Conditions: When the divisor value and the decimal scaling cancel out. In the example below, the divide operation necessitates a decimal left shift by 2, and since the divide by 100 is modelled as the decimal right shift by 2, these operations cancel out.
V4 behavior: Use packed decimal shift (SRP) and divide (DP) instructions
V6 behavior: Divide and decimal scaling are cancelled out so instructions equivalent to a simple MOVE operation are generated
1 p9v0 pic s9(9) comp-3
1 p10v2 pic s9(10)v9(2) comp-3.
COMPUTE p10v2 = p9v0 / 100Performance: V6 is 89% faster than V4
TRUNC(STD) binary arithmetic
Statement: COMPUTE (+ | - | * | /), ADD, SUBTRACT, MULTIPLY, DIVIDE
Data types: BINARY, COMP, COMP-4
Options: TRUNC(STD)
Conditions: In all cases
V4 behavior: Use an expensive divide operation to correct digits back to PIC specification
V6 behavior: Only use divide when actually required (in cases of overflow).
1 b5v2a pic s9(5)v9(2) comp.
1 b5v2b pic s9(5)v9(2) comp.
COMPUTE b5v2a = b5v2a + b5v2bPerformance: V6 is 75% faster than V4
Large binary arithmetic
Statement: COMPUTE (+ | - | * | /), ADD, SUBTRACT, MULTIPLY, DIVIDE
Data types: BINARY, COMP, COMP-4
Options: TRUNC(STD)
Conditions: Intermediate results exceed 9 digits
V4 behavior: Arithmetic performed piecewise and converted to packed decimal
V6 behavior: Arithmetic performed in 64-bit registers
1 b8v2a pic s9(8)v9(2) comp.
1 b8v2b pic s9(9)v9(2) comp.
Compute b8v2a = b8v2a + b8v2b.Performance: V6 is 93% faster than V4
Negation of decimal values
Statement: COMPUTE (-), SUBTRACT
Data types: COMP-3, DISPLAY, NATIONAL
Options: Default
Conditions: In all cases
V4 behavior: Treat as any other subtract from zero
V6 behavior: Recognize as a special case negate operation
1 p7v2a pic s9(7)v9(2) comp-3.
1 p7v2b pic s9(7)v9(2) comp-3.
Compute p7v2b = - p7v2a.Performance: V6 is 26% faster than V4
Fusing DIVIDE GIVING REMAINDER
Statement: DIVIDE
Data types: COMP-3, DISPLAY
Options: OPT(1 | 2)
Conditions: Both the remainder and the quotient of a division are being used
V4 behavior: Separate divide and remainder computations
V6 behavior: Uses a single DP instruction, and recovers both the remainder and the quotient
01 A COMP-3 PIC S9(15).
01 B COMP-3 PIC S9(15).
01 C COMP-3 PIC S9(15).
01 D COMP-3 PIC S9(15).
DIVIDE A BY B GIVING C REMAINDER D
Performance: V6 is 2% faster than V4