DESIGN OF THE IBM RISC SYSTEM-6000 FLOATING-POINT EXECUTION UNIT

被引:102
作者
MONTOYE, RK [1 ]
HOKENEK, E [1 ]
RUNYON, SL [1 ]
机构
[1] IBM CORP,DIV ADV WORKSTN,AUSTIN,TX 78758
关键词
D O I
10.1147/rd.341.0059
中图分类号
TP3 [计算技术、计算机技术];
学科分类号
0812 ;
摘要
The IBM RISC System/6000 (RS/6000) floating-point unit (FPU) exemplifies a second-generation RISC CPU architecture and an implementation which greatly increases floating-point performance and accuracy. The key feature of the FPU is a unified floating-point multiply-add-fused unit (MAF) which performs the accumulate operation (A × B) + C as an indivisible operation. This single functional unit reduces the latency for chained floating-point operations, as well as rounding errors and chip busing. It also reduces the number of adders/normalizers by combining the addition required for fast multiplication with accumulation. The MAF unit is made practical by a unique fast-shifter, which eases the overlap of multiplication and addition, and a leading-zero/one anticipator, which eases overlap of normalization and addition. The accumulate instruction required by this architecture reduces the instruction path length by combining two instructions into one. Additionally, the RS/6000 FPU is tightly coupled to the rest of the CPU, unlike typical floating-point coprocessor chips. As a result, floating-point and fixed-point instructions can be executed simultaneously.
引用
收藏
页码:59 / 70
页数:12
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