A circuit for calculating the fused sum of an addend and product of two multiplication operands, the addend and multiplication operands being binary floating-point numbers represented in a standardized format as a mantissa and an exponent is provided. The multiplication operands are in a lower precision format than the addend, with q>2p, where p and q are the mantissa size of the multiplication operand and addend precision formats. The circuit includes a p-bit multiplier receiving the mantissas of the multiplication operands; a shift circuit aligning the mantissa of the addend with the product output by the multiplier based on the exponent values of the addend and multiplication operands; and an adder processing q-bit mantissas, receiving the aligned mantissa of the addend and the product, the input lines of the adder corresponding to the product being completed to the right by lines at 0 to form a q-bit mantissa.