Arithmetic circuit, arithmetic processing apparatus and method of controlling arithmetic circuit

An arithmetic processing apparatus comprising:

• an arithmetic circuit to round pre-rounded data;
• and
• an instruction control unit to decode a pre-round-processing instruction for controlling pre-round processing performed prior to rounding of a result of arithmetic performed by the arithmetic circuit,
• wherein the arithmetic circuit includes:
• a first input register to store first-format pre-rounded data that includes a mantissa of a fixed-precision floating-point number using a base-N numbering system (N:
• integer larger than or equal to 2), and includes an exponent for the mantissa;
• a second input register to store rounding precision data indicative of precision for rounding the pre-rounded data;
• a first leading zero counting unit to count consecutive zeros starting from a most significant bit of the mantissa stored in the first input register based on a result of decoding the pre-round-processing instruction obtained by the instruction control unit;
• an exponent generating unit to generate a post-round exponent indicative of an exponent for a rounded significant by subtracting the number of zeros counted by the first leading zero counting unit and the rounding precision data from a sum of one and the exponent stored in the first input register, based on the result of decoding the pre-round-processing instruction obtained by the instruction control unit;
• and
• a first output register to store the post-round exponent generated by the exponent generating unit and a rounding-add value that is to be added to a digit at which rounding is performed.

A method of controlling an arithmetic circuit including:

• a first input register to store first-format pre-rounded data that includes a mantissa of a fixed-precision floating-point number using a base-N numbering system (N:
• integer larger than or equal to 2), and includes an exponent for the mantissa;
• and a second input register to store rounding precision data indicative of precision for rounding the pre-rounded data, the method comprising:
• counting, by use of a first leading zero counting unit of the arithmetic circuit, consecutive zeros starting from a most significant bit of the mantissa stored in the first input register;
• and
• generating, by use of an exponent generating unit of the arithmetic circuit, a post-round exponent indicative of an exponent for a rounded significant by subtracting the number of zeros counted by the first leading zero counting unit and the rounding precision data from a sum of one and the exponent stored in the first input register, thereby generating a rounding-add value that is to be added at a digit at which rounding is performed.