Detection of potential need to use a larger data format in performing floating point operations

A method for determining whether a decimal floating point number is safe or unsafe, said method comprising:

• obtaining a machine instruction for execution, the machine instruction comprising an opcode, a register field, an index field, a base field and a displacement value;
• and
• obtaining, by a processor of a processing environment, a first operand in a decimal floating point format, the first operand included in a register specified by the register field;
• performing a function defined by the opcode of the machine instruction of determining whether the first operand is a safe decimal floating point number or is a potentially unsafe decimal floating point number, said function comprising:
• determining a data group and a sign for the first operand;
• determining a plurality of second operand bits using the index field, base field and displacement value of the machine instruction, each bit of the plurality of second operand bits corresponding to a data group and sign combination;
• selecting a bit of the plurality of second operand bits based on the data group and sign determined for the first operand;
• determining a value of the selected bit;
• and
• setting a condition code based on the value of the selected bit, the condition code indicating whether a result of a floating point operation is safe or potentially unsafe
• wherein unsafe indicates that use of a larger data format would produce a different value or quantum.